Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	ATM	Public Stock Offering	Common Stock	Common Stock ATM	Common Stock Public Stock Offering	Additional Paid-in Capital	Additional Paid-in Capital ATM	Additional Paid-in Capital Public Stock Offering	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Balance at beginning of period (in shares) at Dec. 31, 2018				23,234,472
Balance at beginning of period at Dec. 31, 2018	$ 8,795			$ 3			$ 172,966			$ (8)	$ (164,166)
Increase (Decrease) in Stockholders' Equity
Exercise of stock options (in shares)				12,192
Exercise of stock options	42						42
Issuance of common stock under public offering, net of issuance costs (in shares)				24,437,500
Issuance of common stock under public offering, net of issuance costs	92,162			$ 2			92,160
Stock-based compensation expense	1,164						1,164
Other comprehensive income (loss)	8									8
Net (loss) income	21,901										21,901
Balance at end of period (in shares) at Mar. 31, 2019				47,684,164
Balance at end of period at Mar. 31, 2019	124,072			$ 5			266,332				(142,265)
Balance at beginning of period (in shares) at Dec. 31, 2018				23,234,472
Balance at beginning of period at Dec. 31, 2018	8,795			$ 3			172,966			(8)	(164,166)
Increase (Decrease) in Stockholders' Equity
Net (loss) income	(11,962)
Balance at end of period (in shares) at Sep. 30, 2019				47,882,897
Balance at end of period at Sep. 30, 2019	93,045			$ 5			269,140			28	(176,128)
Balance at beginning of period (in shares) at Mar. 31, 2019				47,684,164
Balance at beginning of period at Mar. 31, 2019	124,072			$ 5			266,332				(142,265)
Increase (Decrease) in Stockholders' Equity
Exercise of stock options (in shares)				32,693
Exercise of stock options	58						58
Purchase of common stock under ESPP (in shares)				82,281
Purchase of common stock under ESPP	283						283
Stock-based compensation expense	1,161						1,161
Other comprehensive income (loss)	11									11
Net (loss) income	(17,071)										(17,071)
Balance at end of period (in shares) at Jun. 30, 2019				47,799,138
Balance at end of period at Jun. 30, 2019	108,514			$ 5			267,834			11	(159,336)
Increase (Decrease) in Stockholders' Equity
Exercise of stock options and warrants (in shares)				83,759
Exercise of stock options and warrants	21						21
Stock-based compensation expense	1,285						1,285
Other comprehensive income (loss)	17									17
Net (loss) income	(16,792)										(16,792)
Balance at end of period (in shares) at Sep. 30, 2019				47,882,897
Balance at end of period at Sep. 30, 2019	93,045			$ 5			269,140			28	(176,128)
Increase (Decrease) in Stockholders' Equity
Retirement of common stock in exchange for common stock warrant (in shares)				(2,575,000)
Retirement of common stock in exchange for common stock warrant	(8,986)						(8,986)
Issuance of common stock warrant in exchange for retirement of common stock	8,986						8,986
Purchase of common stock under ESPP (in shares)				57,792
Purchase of common stock under ESPP	206						206
Exercise of stock options and warrants (in shares)				22,334
Exercise of stock options and warrants	54						54
Stock-based compensation expense	1,262						1,262
Other comprehensive income (loss)	(3)									(3)
Net (loss) income	(16,246)										(16,246)
Balance at end of period (in shares) at Dec. 31, 2019				45,388,023
Balance at end of period at Dec. 31, 2019	78,318			$ 5			270,662			25	(192,374)
Increase (Decrease) in Stockholders' Equity
Exercise of stock options (in shares)				43,055
Exercise of stock options	$ 119						119
Exercise of common stock warrant in exchange for common stock (in shares)	0			2,574,971
Stock-based compensation expense	$ 1,609						1,609
Other comprehensive income (loss)	(29)									(29)
Net (loss) income	(16,926)										(16,926)
Balance at end of period (in shares) at Mar. 31, 2020				48,006,049
Balance at end of period at Mar. 31, 2020	63,091			$ 5			272,390			(4)	(209,300)
Balance at beginning of period (in shares) at Dec. 31, 2019				45,388,023
Balance at beginning of period at Dec. 31, 2019	$ 78,318			$ 5			270,662			25	(192,374)
Increase (Decrease) in Stockholders' Equity
Exercise of stock options (in shares)	338,069
Net (loss) income	$ (59,203)
Balance at end of period (in shares) at Sep. 30, 2020				68,470,081
Balance at end of period at Sep. 30, 2020	253,308			$ 7			504,876			0	(251,575)
Balance at beginning of period (in shares) at Mar. 31, 2020				48,006,049
Balance at beginning of period at Mar. 31, 2020	63,091			$ 5			272,390			(4)	(209,300)
Increase (Decrease) in Stockholders' Equity
Exercise of stock options (in shares)				206,143
Exercise of stock options	1,296						1,296
Issuance of common stock under public offering, net of issuance costs (in shares)					10,900,599	9,200,000
Issuance of common stock under public offering, net of issuance costs		$ 62,977	$ 163,991		$ 1	$ 1		$ 62,976	$ 163,990
Purchase of common stock under ESPP (in shares)				68,419
Purchase of common stock under ESPP	333						333
Stock-based compensation expense	1,656						1,656
Other comprehensive income (loss)	6									6
Net (loss) income	(19,786)										(19,786)
Balance at end of period (in shares) at Jun. 30, 2020				68,381,210
Balance at end of period at Jun. 30, 2020	273,564			$ 7			502,641			2	(229,086)
Increase (Decrease) in Stockholders' Equity
Exercise of stock options (in shares)				88,871
Exercise of stock options	317						317
Stock-based compensation expense	1,918						1,918
Other comprehensive income (loss)	(2)									(2)
Net (loss) income	(22,489)										(22,489)
Balance at end of period (in shares) at Sep. 30, 2020				68,470,081
Balance at end of period at Sep. 30, 2020	$ 253,308			$ 7			$ 504,876			$ 0	$ (251,575)