Annual report pursuant to Section 13 and 15(d)

Stockholders' Equity - Narrative (Details)

Stockholders' Equity - Narrative (Details) - USD ($)											1 Months Ended			3 Months Ended									6 Months Ended	12 Months Ended
Stockholders' Equity - Narrative (Details) - USD ($)	Jun. 24, 2018	Dec. 12, 2017	Apr. 11, 2017	Apr. 03, 2017	Mar. 20, 2017	Feb. 13, 2017	Feb. 07, 2017	Nov. 21, 2016	May 24, 2016	May 18, 2016	Jun. 30, 2018	May 31, 2018	Apr. 30, 2018	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2016	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2014	Jun. 18, 2018	Jul. 31, 2017	Mar. 17, 2017	Jun. 07, 2016
Class of Stock [Line Items]
Common stock, authorized (in shares)														50,000,000				50,000,000						50,000,000	50,000,000
Common stock, par value (in dollars per share)														$ 0.001				$ 0.001						$ 0.001	$ 0.001
Convertible note payable														$ 5,000,000				$ 5,000,000						$ 5,000,000	$ 5,000,000
General and administrative expense														$ 6,352,000	$ 2,174,000	$ 3,913,000	$ 1,775,000	$ 1,994,000	$ 1,925,000	$ 1,444,000	$ 1,528,000		$ 400,000	$ 14,214,000	6,891,000	$ 6,610,000
Warrant Exercise Price (in dollars per share)														$ 6.00										$ 6.00
Share Price (in dollars per share)									$ 11.39
Proceeds from issuance of common stock, net of transaction costs																								$ 28,753,000	25,325,000	30,709,000
Maximum Discount Ratio of All Discounts																								99.50%
Allocated transaction cost																									167,000	629,000
Payments of Stock Issuance Costs																								$ 2,096,000
Stock Issued During Period, Value, Issued for Services																								423,000
Exercise of warrants to purchase common stock																								12,500
Incremental fair value																								$ 402,000	$ 0	$ 0
Black-Scholes-Merton assumption, annual dividend rate																								0.00%	0.00%	0.00%
Accrued Liabilities											$ 600,000					$ 600,000							$ 600,000
Modification of Interstate Batteries Warrant 1																								$ 1,002,000
Warrants outstanding to purchase shares, weighted-average exercise price (dollars per share)																								$ 7.31
Number of options granted												420,000												840,000
Weighted-average grant-date fair value (dollars per share)																								$ 1.71	$ 5.55	$ 4.47
Intrinsic value of options																									$ 1,500,000	$ 22,000
Exercise of options to purchase common stock																									$ 1,071,000	$ 19,000
Unrecognized compensation cost														$ 1,700,000										$ 1,700,000
Weighted-average period																									2 years 1 month 6 days
Exercisable period of shares												5 years												2 years 10 months 10 days
Modification of stock awards																									$ 15,000
Additional compensation expense for option modification																						$ 175,000
Granted restricted stock units (RSUs) (in shares)													150,000
Grant fair value													$ 339,000
Granted RSUs, 2017 offering (in shares)														805,749				1,065,003						805,749	1,065,003	443,565
Grant date fair value per share, 2017 offering (dollars per share)														$ 4.57				$ 6.51						$ 4.57	$ 6.51	$ 4.96
11% Convertible Notes
Class of Stock [Line Items]
Convertible note payable														$ 5,000,000										$ 5,000,000
Interest rate														11.00%										11.00%
Maturity date																								May 25, 2019
Conversion price (in dollars per share)														$ 7.12										$ 7.12
Interstate Battery System International, Inc.
Class of Stock [Line Items]
Allocated value									$ 10,000,000
Basis for effective rate									The difference between the face value of the convertible note and the allocated amount (which considers both the allocated fair value of the issued stock and allocated fair value of the warrants) was recorded as an initial discount to the convertible note; common stock was recorded at its allocated fair value as a credit to par value and additional paid-in capital as appropriate, based on the number of shares issued, and the allocated fair value of the warrant was credited to additional paid-in capital. After taking into consideration the amortization of the note discount, the effective interest rate on the convertible note is 184.75% per annum.
Interstate Battery System International, Inc. \| Credit Agreement
Class of Stock [Line Items]
Warrant Exercise Price (in dollars per share)														$ 3.33										$ 3.33
Terms of conversion feature										If Interstate converts its convertible note and exercises both warrants in their entirety, it will own approximately 8.3% of the Company’s common stock at an average price per share of approximately $7.22.
Amortized period to interest expense										3 years
Interstate Battery System International, Inc. \| Credit Agreement \| 11% Convertible Notes
Class of Stock [Line Items]
Maturity date										May 24, 2019
Interstate Battery System International, Inc. \| Securities Purchase Agreement
Class of Stock [Line Items]
Common stock issued (in shares)										702,247
Share Price (in dollars per share)										$ 7.12
Proceeds from issuance of common stock, net of transaction costs										$ 5,000,000
Interstate Battery System International, Inc. \| Interstate Battery System International, Inc.
Class of Stock [Line Items]
Cost allocated										771,000
Debt issuance costs										142,000
Allocated transaction cost										$ 629,000
National Securities Corporation (Placement Agent) \| Definitive Agreements
Class of Stock [Line Items]
Allocated transaction cost																								$ 345,000
Percentage of sales commision																								6.00%
Payments of Stock Issuance Costs																								$ 307,000
Legal Fees																								$ 38,000
Johnson Controls \| Securities Purchase Agreement
Class of Stock [Line Items]
Share Price (in dollars per share)							$ 11.33
Proceeds from issuance of common stock, net of transaction costs							$ 10,600,000
Legal Fees							$ 167,000
Secured Debt \| Interstate Battery System International, Inc. \| Credit Agreement
Class of Stock [Line Items]
General and administrative expense																									$ 600,000
Warrant 1 \| Interstate Battery System International, Inc.
Class of Stock [Line Items]
Warrant shares issued (in shares)														702,247										702,247
Warrant Exercise Price (in dollars per share)														$ 7.12										$ 7.12
Share Price (in dollars per share)														$ 11.39										$ 11.39
Volatility rate																								65.70%
Annual dividend rate																								0.00%
Post-modification exercise price of warrants (dollars per share)														3.33										3.33
Incremental fair value	$ 1,000,000
Black-Scholes-Merton assumption, per share fair value	$ 3.26
Black-Scholes-Merton assumption, term	2 years
Black-Scholes-Merton assumption, volatility	80.20%
Black-Scholes-Merton assumption, discount rate	2.56%
Black-Scholes-Merton assumption, annual dividend rate	0.00%
Warrant 1 \| Secured Debt \| Interstate Battery System International, Inc. \| Credit Agreement
Class of Stock [Line Items]
Expiration Date										May 24, 2018
Warrant 2 \| Interstate Battery System International, Inc.
Class of Stock [Line Items]
Warrant shares issued (in shares)														1,605,131										1,605,131
Warrant Exercise Price (in dollars per share)														$ 9.00										$ 9.00
Share Price (in dollars per share)														$ 11.39										$ 11.39
Volatility rate																								67.80%
Annual dividend rate																								0.00%
Warrant 2 \| Secured Debt \| Interstate Battery System International, Inc. \| Credit Agreement
Class of Stock [Line Items]
Expiration Date										May 24, 2019
Warrant
Class of Stock [Line Items]
Warrant Exercise Price (in dollars per share)			$ 6.00	$ 0.0034375	$ 3.00	$ 3.00																								$ 6.00	$ 6.00
Share Price (in dollars per share)			$ 17.920	$ 19.148	$ 20.304	$ 13.062																								$ 20.262	$ 12.16
Cashless exercise of warrants (in shares)			8,315	43,628	192,666	19,349
Number of warrants exercised			12,500	43,636	226,068	25,119												1,461,744							1,461,744					2,500	30,000
Cash and cashless exercise of warrants (in shares)																									1,175,796
Merrill Lynch US High Yield CCC Rate \| Interstate Battery System International, Inc.
Class of Stock [Line Items]
Weighted average discount rate, percent									16.21%
Merrill Lynch US High Yield B \| Interstate Battery System International, Inc.
Class of Stock [Line Items]
Weighted average discount rate, percent									7.44%
Accredited Investor \| National Securities Corporation (Placement Agent) \| Definitive Agreements
Class of Stock [Line Items]
Common stock issued (in shares)										719,333
Share Price (in dollars per share)										$ 7.12
Proceeds from common stock issued										$ 5,100,000
2016 Public Offering
Class of Stock [Line Items]
Proceeds from common stock issued																										$ 21,542,000
Sale of stock (dollars per share)								$ 10.00
Common stock issued in November 2016 public offering, net of $1,688 offering costs								$ 21,500,000
2016 Public Offering \| Underwriter
Class of Stock [Line Items]
Fees paid								$ 1,400,000
2016 Public Offering \| Underwriter \| Warrant
Class of Stock [Line Items]
Warrant shares issued (in shares)														33,450										33,450
Expiration Date								Nov. 21, 2019
Warrant Exercise Price (in dollars per share)								$ 10.00
Share Price (in dollars per share)								$ 12.66
Class of Warrant or Right, Date from which Warrants or Rights Exercisable								May 20, 2017
Fair value of warrant issued								$ 229,000
Expected term, in years								3 years
Volatility rate								72.00%
Discount rate, fair value inputs								1.36%
Annual dividend rate								0.00%
Johnson Controls Agreement
Class of Stock [Line Items]
Proceeds from common stock issued																									$ 10,472,000
2017 Public Offering
Class of Stock [Line Items]
Proceeds from common stock issued																									13,759,000
Sale of stock (dollars per share)		$ 2.10
Proceeds from common stock issued in December 2017 public offering, net of $1,256 transaction cost		$ 13,800,000
Over-Allotment Option
Class of Stock [Line Items]
Proceeds from common stock issued																								$ 2,103,000
2018 Public Offering
Class of Stock [Line Items]
Proceeds from common stock issued																								26,646,000
Officers and Directors Plan
Class of Stock [Line Items]
Proceeds from common stock issued																								$ 4,000	$ 8,000
Interstate Battery System International, Inc. \| Warrant
Class of Stock [Line Items]
Warrant shares issued (in shares)														2,307,378										2,307,378
Common Stock
Class of Stock [Line Items]
Common stock issued for consulting services (in shares)																								152,727
Cashless exercise of warrants (in shares)																									1,173,296	15,203
Common Stock \| 2016 Public Offering
Class of Stock [Line Items]
Common stock issued (in shares)																										2,300,000
Proceeds from common stock issued																										$ 2,000
Common stock issued in November 2016 public offering, net of $1,688 offering costs (in shares)								2,300,000
Common Stock \| Johnson Controls Agreement
Class of Stock [Line Items]
Common stock issued (in shares)																									939,005
Proceeds from common stock issued																									$ 1,000
Common Stock \| 2017 Public Offering
Class of Stock [Line Items]
Common stock issued (in shares)																									7,150,000
Proceeds from common stock issued																									$ 7,000
Common stock issued in December 2017 public offering, net of $1,256 transaction cost (in shares)		7,150,000
Common Stock \| Over-Allotment Option
Class of Stock [Line Items]
Common stock issued (in shares)																								1,072,500
Proceeds from common stock issued																								$ 2,000
Common Stock \| 2018 Public Offering
Class of Stock [Line Items]
Common stock issued (in shares)																								10,085,500
Proceeds from common stock issued																								$ 10,000
Sale of stock (dollars per share)																												$ 2.85
Proceeds from initial public offering											$ 28,700,000
Common Stock \| Officers and Directors Plan
Class of Stock [Line Items]
Common stock issued (in shares)																								2,034	2,404
Proceeds from common stock issued																								$ 0
Additional Paid-in Capital
Class of Stock [Line Items]
Stock Issued During Period, Value, Issued for Services																								423,000
Modification of Interstate Batteries Warrant 1																								1,002,000
Exercise of options to purchase common stock																									$ 1,071,000	19,000
Additional Paid-in Capital \| 2016 Public Offering
Class of Stock [Line Items]
Proceeds from common stock issued																										$ 21,540,000
Additional Paid-in Capital \| Johnson Controls Agreement
Class of Stock [Line Items]
Proceeds from common stock issued																									10,471,000
Additional Paid-in Capital \| 2017 Public Offering
Class of Stock [Line Items]
Proceeds from common stock issued																									13,752,000
Additional Paid-in Capital \| Over-Allotment Option
Class of Stock [Line Items]
Proceeds from common stock issued																								2,101,000
Additional Paid-in Capital \| 2018 Public Offering
Class of Stock [Line Items]
Proceeds from common stock issued																								26,636,000
Additional Paid-in Capital \| Officers and Directors Plan
Class of Stock [Line Items]
Proceeds from common stock issued																								4,000	$ 8,000
2014 Stock Incentive Plan
Class of Stock [Line Items]
Common stock authorized for issuance (in shares)																											2,113,637
Option award expiration date																											10 years
Unrecognized compensation cost														$ 11,000										$ 11,000
Weighted-average period																								11 days
Option 1
Class of Stock [Line Items]
Exercise price (dollars per share)												$ 3.00
Option 2
Class of Stock [Line Items]
Number of options granted												210,000
Exercise price (dollars per share)												$ 5.00
Exercisable period of shares												5 years
Option 3
Class of Stock [Line Items]
Number of options granted												210,000
Exercise price (dollars per share)												$ 7.00
Exercisable period of shares												5 years
Restricted Stock (in shares)
Class of Stock [Line Items]
Grant date fair value per share, 2017 offering (dollars per share)														$ 4.01				$ 7.40						$ 4.01	$ 7.40	$ 0
Restricted Stock Units (RSUs)
Class of Stock [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Vested																								$ 100,000
Intrinsic value, outstanding options														$ 200,000										$ 200,000
Restricted Stock Units (RSUs) \| Common Stock
Class of Stock [Line Items]
Common stock issued (in shares)																								65,600
Chief Financial Officer \| Restricted Stock Units (RSUs) \| Employment Agreement
Class of Stock [Line Items]
Granted RSUs, 2017 offering (in shares)																													49,751
Grant date fair value per share, 2017 offering (dollars per share)																													$ 11.68
Minimum
Class of Stock [Line Items]
Black-Scholes-Merton assumption, term												90 days												2 years 6 months	2 years 6 months	2 years 6 months
Black-Scholes-Merton assumption, volatility																								76.90%	70.50%	71.00%
Maximum
Class of Stock [Line Items]
Black-Scholes-Merton assumption, term												2 years												3 years 6 months	3 years 6 months	4 years
Black-Scholes-Merton assumption, volatility																								86.30%	73.20%	80.00%
Scenario, Previously Reported
Class of Stock [Line Items]
General and administrative expense																									$ 600,000