Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Total
Stockholders' Equity, Beginning Balance at Dec. 31, 2018	$ 32	$ 315,598	$ (133)	$ (269,051)	$ 46,446
Shares, Outstanding, Beginning Balance at Dec. 31, 2018	32,364,895
Exercises of vested stock options	$ 1	283			284
Exercises of vested stock options (in shares)	31,360
Issuance of common stock in connection with Neurocrine Collaboration Agreement	$ 4	77,613			77,617
Issuance of common stock in connection with Neurocrine Collaboration Agreement (in shares)	4,179,728
Stock based compensation expense		3,459			3,459
Unrealized gain on available for-sale securities, net of tax			58		58
Net loss				(27,170)	(27,170)
Stockholders' Equity, Ending Balance at Mar. 31, 2019	$ 37	396,953	(75)	(296,221)	100,694
Shares, Outstanding, Ending Balance at Mar. 31, 2019	36,575,983
Stockholders' Equity, Beginning Balance at Dec. 31, 2019	$ 37	412,227	(104)	(312,648)	99,512
Shares, Outstanding, Beginning Balance at Dec. 31, 2019	36,865,116
Vesting of restricted stock units (in shares)	108,600
Exercises of vested stock options		34			$ 34
Exercises of vested stock options (in shares)	3,035				3,035
Stock based compensation expense		3,949			$ 3,949
Unrealized gain on available for-sale securities, net of tax			525		525
Net loss				(24,263)	(24,263)
Stockholders' Equity, Ending Balance at Mar. 31, 2020	$ 37	$ 416,210	$ 421	$ (336,911)	$ 79,757
Shares, Outstanding, Ending Balance at Mar. 31, 2020	36,976,751