Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning Balance at Dec. 31, 2018	$ 146,006	$ 8	$ 741,246	$ (267)	$ (594,981)
Beginning Balance, Shares at Dec. 31, 2018		79,087,734
Stock-based compensation expense	1,873	$ 0	1,873	0	0
Exercise of warrants	35,151	$ 2	35,149	0	0
Exercise of warrants, Shares		17,589,250
Exercise of stock options	4,070	$ 0	4,070	0	0
Exercise of stock options, Shares		1,986,300
Vesting of restricted stock units (RSUs)	0	$ 0	0	0	0
Vesting of restricted stock units (RSUs), Shares		157,291
Employee payroll taxes withheld related to vesting of RSUs and exercise of stock options	(26)	$ 0	(26)	0	0
Employee payroll taxes withheld related to vesting of RSUs and exercise of stock options, Shares		(39,130)
Cumulative effect of the adoption of the new lease standard | Accounting Standards Update 2016-02	(920)	$ 0	0	0	(920)
Repurchase of common stock	$ (501)	$ 0	0	0	(501)
Repurchase of common stock, Shares	(473,586)	(473,586)
Other comprehensive income, net	$ 183	$ 0	0	183	0
Net loss	(34,567)	0	0	0	(34,567)
Ending Balance at Jun. 30, 2019	151,269	$ 10	782,312	(84)	(630,969)
Ending Balance, Shares at Jun. 30, 2019		98,307,859
Beginning Balance at Mar. 31, 2019	167,808	$ 10	781,790	(206)	(613,786)
Beginning Balance, Shares at Mar. 31, 2019		98,674,153
Stock-based compensation expense	522	$ 0	522	0	0
Vesting of restricted stock units (RSUs)	0	$ 0	0	0	0
Vesting of restricted stock units (RSUs), Shares		107,516
Employee payroll taxes withheld related to vesting of RSUs and exercise of stock options	0	$ 0	0	0	0
Employee payroll taxes withheld related to vesting of RSUs and exercise of stock options, Shares		(224)
Repurchase of common stock	$ (501)	$ 0	0	0	(501)
Repurchase of common stock, Shares	(473,586)	(473,586)
Other comprehensive income, net	$ 122	$ 0	0	122	0
Net loss	(16,682)	0	0	0	(16,682)
Ending Balance at Jun. 30, 2019	151,269	$ 10	782,312	(84)	(630,969)
Ending Balance, Shares at Jun. 30, 2019		98,307,859
Beginning Balance at Dec. 31, 2019	$ 120,679	$ 10	782,965	(105)	(662,191)
Beginning Balance, Shares at Dec. 31, 2019	98,460,404	98,460,404
Issuance of common stock, net	$ 86,282	$ 1	86,281	0	0
Issuance of common stock, net, Shares		8,521,500
Stock-based compensation expense	761	$ 0	761	0	0
Exercise of stock options	564	$ 0	564	0	0
Exercise of stock options, Shares		259,017
Vesting of restricted stock units (RSUs)	0	$ 0	0	0	0
Vesting of restricted stock units (RSUs), Shares		558,976
Employee payroll taxes withheld related to vesting of RSUs and exercise of stock options	$ (163)	$ 0	(163)	0	0
Employee payroll taxes withheld related to vesting of RSUs and exercise of stock options, Shares		(35,739)
Repurchase of common stock, Shares	0
Other comprehensive income, net	$ 5	$ 0	0	5	0
Net loss	(38,475)	0	0	0	(38,475)
Ending Balance at Jun. 30, 2020	$ 169,653	$ 11	870,408	(100)	(700,666)
Ending Balance, Shares at Jun. 30, 2020	107,764,158	107,764,158
Beginning Balance at Mar. 31, 2020	$ 102,595	$ 10	783,287	(128)	(680,574)
Beginning Balance, Shares at Mar. 31, 2020		98,498,432
Issuance of common stock, net	86,282	$ 1	86,281	0	0
Issuance of common stock, net, Shares		8,521,500
Stock-based compensation expense	316	$ 0	316	0	0
Exercise of stock options	564	$ 0	564	0	0
Exercise of stock options, Shares		259,017
Vesting of restricted stock units (RSUs)	0	$ 0	0	0	0
Vesting of restricted stock units (RSUs), Shares		495,226
Employee payroll taxes withheld related to vesting of RSUs and exercise of stock options	$ (40)	$ 0	(40)	0	0
Employee payroll taxes withheld related to vesting of RSUs and exercise of stock options, Shares		(10,017)
Repurchase of common stock, Shares	0
Other comprehensive income, net	$ 28	$ 0	0	28	0
Net loss	(20,092)	0	0	0	(20,092)
Ending Balance at Jun. 30, 2020	$ 169,653	$ 11	$ 870,408	$ (100)	$ (700,666)
Ending Balance, Shares at Jun. 30, 2020	107,764,158	107,764,158