Condensed Consolidated Statements of Stockholders’ Equity - USD ($) $ in Thousands	Common stock	Additional Paid-in Capital	Accumulated Deficit	Total
Beginning balance at Dec. 31, 2017	$ 27	$ 255,013	$ (110,252)	$ 144,788
Beginning balance (in shares) at Dec. 31, 2017	27,284,140
Increase (Decrease) in Stockholders' Equity
Stock compensation expense		958		958
Shares issued for license agreement		4,448		4,448
Change in unrealized loss on marketable securities		(77)		(77)
Net loss			(16,459)	(16,459)
Ending balance at Mar. 31, 2018	$ 27	260,342	(126,711)	133,658
Ending balance (in shares) at Mar. 31, 2018	27,284,140
Beginning balance at Dec. 31, 2017	$ 27	255,013	(110,252)	144,788
Beginning balance (in shares) at Dec. 31, 2017	27,284,140
Increase (Decrease) in Stockholders' Equity
Net loss				(30,871)
Ending balance at Jun. 30, 2018	$ 34	425,406	(141,123)	284,317
Ending balance (in shares) at Jun. 30, 2018	34,173,137
Beginning balance at Mar. 31, 2018	$ 27	260,342	(126,711)	133,658
Beginning balance (in shares) at Mar. 31, 2018	27,284,140
Increase (Decrease) in Stockholders' Equity
Stock compensation expense		1,516		1,516
Shares issued for license agreement (in shares)	223,544
Issuance of common stock upon completion of public offering, net of offering costs	$ 7	163,027		163,034
Issuance of common stock upon completion of public offering, net of offering costs (in shares)	6,591,800
Issuance of common stock in connection with exercise of stock options		399		399
Issuance of common stock in connection with exercise of stock options (in shares)	73,653
Change in unrealized loss on marketable securities		122		122
Net loss			(14,412)	(14,412)
Ending balance at Jun. 30, 2018	$ 34	425,406	(141,123)	284,317
Ending balance (in shares) at Jun. 30, 2018	34,173,137
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
Change in unrealized loss 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
Change in unrealized loss 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