CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income	Accumulated Deficit	Total
Beginning balance at Dec. 31, 2018	$ 34	$ 430,824		$ (184,602)	$ 246,256
Beginning balance (in shares) at Dec. 31, 2018	34,410,725
Increase (Decrease) in Stockholders' Equity
Stock compensation expense		2,644			2,644
Issuance of common stock in connection with ESPP		295			295
Issuance of common stock in connection with ESPP (in shares)	12,105
Issuance of common stock in connection with exercise of stock options		54			54
Issuance of common stock in connection with exercise of stock options (in shares)	7,811
Unrealized gain on marketable securities		214			214
Net loss				(28,974)	(28,974)
Ending balance at Mar. 31, 2019	$ 34	434,031		(213,576)	220,489
Ending balance (in shares) at Mar. 31, 2019	34,430,641
Beginning balance at Dec. 31, 2018	$ 34	430,824		(184,602)	246,256
Beginning balance (in shares) at Dec. 31, 2018	34,410,725
Increase (Decrease) in Stockholders' Equity
Net loss					(71,770)
Ending balance at Jun. 30, 2019	$ 34	437,805		(256,372)	181,467
Ending balance (in shares) at Jun. 30, 2019	34,497,542
Beginning balance at Mar. 31, 2019	$ 34	434,031		(213,576)	220,489
Beginning balance (in shares) at Mar. 31, 2019	34,430,641
Increase (Decrease) in Stockholders' Equity
Stock compensation expense		3,272			3,272
Issuance of common stock in connection with exercise of stock options		465			465
Issuance of common stock in connection with exercise of stock options (in shares)	66,901
Unrealized gain on marketable securities		37			37
Net loss				(42,796)	(42,796)
Ending balance at Jun. 30, 2019	$ 34	437,805		(256,372)	181,467
Ending balance (in shares) at Jun. 30, 2019	34,497,542
Beginning balance at Dec. 31, 2019
Beginning balance at Dec. 31, 2019	$ 44	606,307		(325,331)	281,020
Beginning balance (in shares) at Dec. 31, 2019	43,996,753
Increase (Decrease) in Stockholders' Equity
Stock compensation expense		5,475			5,475
Issuance of common stock in connection with ESPP		324			324
Issuance of common stock in connection with ESPP (in shares)	18,673
Issuance of common stock in connection with exercise of stock options		383			383
Issuance of common stock in connection with exercise of stock options (in shares)	72,964
Unrealized gain on marketable securities			$ 63		63
Net loss				(34,164)	(34,164)
Ending balance at Mar. 31, 2020	$ 44	612,489	63	(359,495)	253,101
Ending balance (in shares) at Mar. 31, 2020	44,088,390
Beginning balance at Dec. 31, 2019
Ending balance at Jun. 30, 2020
Beginning balance at Dec. 31, 2019	$ 44	606,307		(325,331)	281,020
Beginning balance (in shares) at Dec. 31, 2019	43,996,753
Increase (Decrease) in Stockholders' Equity
Net loss					(65,281)
Ending balance at Jun. 30, 2020	$ 44	615,691	630	(390,612)	225,753
Ending balance (in shares) at Jun. 30, 2020	44,115,612
Ending balance at Jun. 30, 2020
Beginning balance at Mar. 31, 2020	$ 44	612,489	63	(359,495)	253,101
Beginning balance (in shares) at Mar. 31, 2020	44,088,390
Increase (Decrease) in Stockholders' Equity
Stock compensation expense		3,028			3,028
Issuance of common stock in connection with exercise of stock options		174			174
Issuance of common stock in connection with exercise of stock options (in shares)	27,222
Unrealized gain on marketable securities			567		567
Net loss				(31,117)	(31,117)
Ending balance at Jun. 30, 2020	$ 44	$ 615,691	$ 630	$ (390,612)	$ 225,753
Ending balance (in shares) at Jun. 30, 2020	44,115,612