Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Preferred Stock	Common stock	Additional paid-in Capital	Accumulated other comprehensive income (loss)	Accumulated deficit	Total
Balance at Dec. 31, 2017		$ 1	$ 288,750	$ (31)	$ (106,461)	$ 182,259
Balance (in shares) at Dec. 31, 2017	1,969,797	14,227,634
Increase (Decrease) in Stockholders' Equity
Exercise of common stock options			265			265
Exercise of common stock options (in shares)		23,092
Compensation expense related to stock options for services			1,167			1,167
Unrealized loss on marketable securities				(143)		(143)
Net loss					(6,364)	(6,364)
Balance at Mar. 31, 2018		$ 1	290,182	(174)	(112,825)	177,184
Balance (in shares) at Mar. 31, 2018	1,969,797	14,250,726
Balance at Dec. 31, 2018		$ 2	616,573	(319)	(139,272)	$ 476,984
Balance (in shares) at Dec. 31, 2018	1,969,797	15,409,023				15,409,023
Increase (Decrease) in Stockholders' Equity
Exercise of common stock options			83			$ 83
Exercise of common stock options (in shares)		8,041
Compensation expense related to stock options for services			6,022			6,022
Unrealized loss on marketable securities				497		497
Net loss					(15,080)	(15,080)
Balance at Mar. 31, 2019		$ 2	$ 622,678	$ 178	$ (154,352)	$ 468,506
Balance (in shares) at Mar. 31, 2019	1,969,797	15,417,064				15,417,064