Quarterly report pursuant to Section 13 or 15(d)

Condensed Consolidated Statements of Stockholders' Equity (Deficit)

Condensed Consolidated Statements of Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	May 2019 Public Offering	January 2019 Public Offering	Over-Allotment Option	2018 Public Offering	Officers and Directors Purchase Plan	Common Stock	Common Stock May 2019 Public Offering	Common Stock January 2019 Public Offering	Common Stock Over-Allotment Option	Common Stock 2018 Public Offering	Common Stock Restricted Stock Units (RSUs)	Common Stock Officers and Directors Purchase Plan	Additional Paid-in Capital	Additional Paid-in Capital May 2019 Public Offering	Additional Paid-in Capital January 2019 Public Offering	Additional Paid-in Capital Over-Allotment Option	Additional Paid-in Capital 2018 Public Offering	Additional Paid-in Capital Officers and Directors Purchase Plan	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2017							27,554,076
Beginning balance at Dec. 31, 2017	$ 58,965						$ 27							$ 113,780						$ (54,842)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	492													492
Common stock issued during period (in shares)										1,072,500	10,085,500	65,600	2,034
Common stock issued during period				$ 2,103	$ 26,647	$ 4				$ 2	$ 10						$ 2,101	$ 26,637	$ 4
Modification of Interstate Battery warrant 1	1,002													1,002
Net loss	(17,459)																			(17,459)
Ending balance (in shares) at Jun. 30, 2018							38,779,710
Ending Balance at Jun. 30, 2018	71,754						$ 39							144,016						(72,301)
Beginning balance (in shares) at Mar. 31, 2018							28,694,210
Beginning balance at Mar. 31, 2018	53,684						$ 29							116,029						(62,374)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	348													348
Common stock issued during period (in shares)											10,085,500
Common stock issued during period					$ 26,647						$ 10							$ 26,637
Modification of Interstate Battery warrant 1	1,002													1,002
Net loss	(9,927)																			(9,927)
Ending balance (in shares) at Jun. 30, 2018							38,779,710
Ending Balance at Jun. 30, 2018	71,754						$ 39							144,016						(72,301)
Beginning balance (in shares) at Dec. 31, 2018							38,932,437
Beginning balance at Dec. 31, 2018	50,090						$ 39							145,147						(95,096)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	1,998													1,998
Warrants related to Veolia agreement	2,312													2,312
Common stock issued during period (in shares)								11,000,000	5,175,000			357,168
Common stock issued during period		$ 20,317	$ 9,063					$ 11	$ 5						$ 20,306	$ 9,058
Common stock issued for consulting services (in shares)							1,425,271
Common stock issued for consulting services	3,044						$ 2							3,042
Net loss	(22,209)																			(22,209)
Ending balance (in shares) at Jun. 30, 2019							56,889,876
Ending Balance at Jun. 30, 2019	64,615						$ 57							181,863						(117,305)
Beginning balance (in shares) at Mar. 31, 2019							44,727,697
Beginning balance at Mar. 31, 2019	50,278						$ 45							157,037						(106,804)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	930													930
Warrants related to Veolia agreement	1,734													1,734
Common stock issued during period (in shares)												39,350
Common stock issued during period	0
Common stock issued for consulting services (in shares)							1,122,829	11,000,000
Common stock issued for consulting services	1,857	$ 20,317					$ 1	$ 11						1,856	$ 20,306
Net loss	(10,501)																			(10,501)
Ending balance (in shares) at Jun. 30, 2019							56,889,876
Ending Balance at Jun. 30, 2019	$ 64,615						$ 57							$ 181,863						$ (117,305)