Condensed Consolidated Statements of Stockholders' (Deficit) Equity - USD ($) $ in Thousands	Common stock	Additional paid-in capital	Accumulated other comprehensive income/(loss)	Accumulated deficit	Total
Balance at beginning of period (in shares) at Dec. 31, 2017	22,765,017
Balance at beginning of period at Dec. 31, 2017	$ 3	$ 168,018	$ (149)	$ (97,878)	$ 69,994
Increase (Decrease) in Stockholders' Equity
Cumulative effect adjustment for adoption of ASC 606				(2,031)	(2,031)
Exercise of stock options (in shares)	104,945
Exercise of stock options		255			255
Stock-based compensation expense		745			745
Other comprehensive income (loss)			(13)		(13)
Net (loss) income				(12,403)	(12,403)
Balance at end of period (in shares) at Mar. 31, 2018	22,869,962
Balance at end of period at Mar. 31, 2018	$ 3	169,018	(162)	(112,312)	56,547
Balance at beginning of period (in shares) at Dec. 31, 2017	22,765,017
Balance at beginning of period at Dec. 31, 2017	$ 3	168,018	(149)	(97,878)	69,994
Increase (Decrease) in Stockholders' Equity
Cumulative effect adjustment for adoption of ASC 606					(2,031)
Net (loss) income					(41,825)
Balance at end of period (in shares) at Sep. 30, 2018	23,160,875
Balance at end of period at Sep. 30, 2018	$ 3	171,627	(42)	(141,735)	29,853
Balance at beginning of period (in shares) at Mar. 31, 2018	22,869,962
Balance at beginning of period at Mar. 31, 2018	$ 3	169,018	(162)	(112,312)	56,547
Increase (Decrease) in Stockholders' Equity
Exercise of stock options (in shares)	247,776
Exercise of stock options		470			470
Stock-based compensation expense		958			958
Other comprehensive income (loss)			72		72
Net (loss) income				(12,354)	(12,354)
Balance at end of period (in shares) at Jun. 30, 2018	23,117,738
Balance at end of period at Jun. 30, 2018	$ 3	170,446	(90)	(124,666)	45,693
Increase (Decrease) in Stockholders' Equity
Exercise of stock options (in shares)	43,137
Exercise of stock options		128			128
Stock-based compensation expense		1,053			1,053
Other comprehensive income (loss)			48		48
Net (loss) income				(17,069)	(17,069)
Balance at end of period (in shares) at Sep. 30, 2018	23,160,875
Balance at end of period at Sep. 30, 2018	$ 3	171,627	(42)	(141,735)	29,853
Increase (Decrease) in Stockholders' Equity
Exercise of stock options (in shares)	31,411
Exercise of stock options		65			65
Purchase of common stock under ESPP (in shares)	42,186
Purchase of common stock under ESPP		146			146
Stock-based compensation expense		1,128			1,128
Other comprehensive income (loss)			34		34
Net (loss) income				(22,431)	(22,431)
Balance at end of period (in shares) at Dec. 31, 2018	23,234,472
Balance at end of period at Dec. 31, 2018	$ 3	172,966	(8)	(164,166)	8,795
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	$ 2	92,160			92,162
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	$ 5	266,332		(142,265)	124,072
Balance at beginning of period (in shares) at Dec. 31, 2018	23,234,472
Balance at beginning of period at Dec. 31, 2018	$ 3	172,966	(8)	(164,166)	$ 8,795
Increase (Decrease) in Stockholders' Equity
Exercise of stock options (in shares)					58,964
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	$ 5	269,140	28	(176,128)	93,045
Balance at beginning of period (in shares) at Mar. 31, 2019	47,684,164
Balance at beginning of period at Mar. 31, 2019	$ 5	266,332		(142,265)	124,072
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	$ 5	267,834	11	(159,336)	108,514
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	$ 5	$ 269,140	$ 28	$ (176,128)	$ 93,045