Condensed Consolidated Statements of Stockholders’ Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Total
Balance at beginning of period at Dec. 31, 2018	$ 3	$ 172,966	$ (8)	$ (164,166)	$ 8,795
Balance at beginning of period (in shares) at Dec. 31, 2018	23,234,472
Increase (Decrease) in Stockholders' Equity
Exercise of stock options		42			42
Exercise of stock options (in shares)	12,192
Issuance of common stock under public offering, net of issuance costs of $5,587	$ 2	92,160			92,162
Issuance of common stock under public offering, net of issuance costs of $5,587 (in shares)	24,437,500
Stock-based compensation expense		1,164			1,164
Other comprehensive income (loss)			8		8
Net income (loss)				21,901	21,901
Balance at end of period at Mar. 31, 2019	$ 5	266,332		(142,265)	124,072
Balance at end of period (in shares) at Mar. 31, 2019	47,684,164
Increase (Decrease) in Stockholders' Equity
Exercise of stock options		58			58
Exercise of stock options (in shares)	32,693
Purchase of common stock under ESPP		283			283
Purchase of common stock under ESPP (in shares)	82,281
Stock-based compensation expense		1,161			1,161
Other comprehensive income (loss)			11		11
Net income (loss)				(17,071)	(17,071)
Balance at end of period at Jun. 30, 2019	$ 5	267,834	11	(159,336)	108,514
Balance at end of period (in shares) at Jun. 30, 2019	47,799,138
Increase (Decrease) in Stockholders' Equity
Exercise of stock options and warrants		21			21
Exercise of stock options and warrants (in shares)	83,759
Stock-based compensation expense		1,285			1,285
Other comprehensive income (loss)			17		17
Net income (loss)				(16,792)	(16,792)
Balance at end of period at Sep. 30, 2019	$ 5	269,140	28	(176,128)	93,045
Balance at end of period (in shares) at Sep. 30, 2019	47,882,897
Increase (Decrease) in Stockholders' Equity
Retirement of common stock in exchange for common stock warrant		(8,986)			(8,986)
Retirement of common stock in exchange for common stock warrant (in shares)	(2,575,000)
Issuance of common stock warrant in exchange for retirement of common stock		8,986			8,986
Purchase of common stock under ESPP		206			206
Purchase of common stock under ESPP (in shares)	57,792
Exercise of stock options and warrants		54			54
Exercise of stock options and warrants (in shares)	22,334
Stock-based compensation expense		1,262			1,262
Other comprehensive income (loss)			(3)		(3)
Net income (loss)				(16,246)	(16,246)
Balance at end of period at Dec. 31, 2019	$ 5	270,662	25	(192,374)	$ 78,318
Balance at end of period (in shares) at Dec. 31, 2019	45,388,023
Increase (Decrease) in Stockholders' Equity
Exercise of stock options (in shares)					43,055
Exercise of common stock warrant in exchange for common stock (in shares)	2,574,971
Exercise of stock options and warrants		119			$ 119
Exercise of stock options and warrants (in shares)	43,055
Stock-based compensation expense		1,609			1,609
Other comprehensive income (loss)			(29)		(29)
Net income (loss)				(16,926)	(16,926)
Balance at end of period at Mar. 31, 2020	$ 5	$ 272,390	$ (4)	$ (209,300)	$ 63,091
Balance at end of period (in shares) at Mar. 31, 2020	48,006,049