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, 2017	$ 32	$ 295,019	$ (287)	$ (160,713)	$ 134,051
Shares, Outstanding, Beginning Balance at Dec. 31, 2017	31,572,044
Vesting of restricted stock		3			3
Vesting of restricted stock (in shares)	145,829
Exercises of vested stock options		1,412			1,412
Exercises of vested stock options (in shares)	132,733
Issuance of common stock under ESPP		418			418
Issuance of common stock under ESPP (in shares)	38,392
Stock based compensation expense		2,260			2,260
Life-to-date cumulative catchup on equity securities			120		120
Unrealized gain (loss) on available for-sale securities, net of tax			5		5
Impact of adopting new accounting standards | ASU 2014-09				(20,050)	(20,050)
Net loss				(19,926)	(19,926)
Stockholders' Equity, Ending Balance at Mar. 31, 2018	$ 32	299,112	(162)	(200,689)	98,293
Shares, Outstanding, Ending Balance at Mar. 31, 2018	31,888,998
Stockholders' Equity, Beginning Balance at Dec. 31, 2017	$ 32	295,019	(287)	(160,713)	134,051
Shares, Outstanding, Beginning Balance at Dec. 31, 2017	31,572,044
Unrealized gain (loss) on available for-sale securities, net of tax					(7)
Impact of adopting new accounting standards | ASU 2016-01					120
Impact of adopting new accounting standards | ASU 2014-09					(20,050)
Net loss					(65,757)
Stockholders' Equity, Ending Balance at Sep. 30, 2018	$ 32	312,250	(174)	(246,519)	65,589
Shares, Outstanding, Ending Balance at Sep. 30, 2018	32,309,700
Stockholders' Equity, Beginning Balance at Mar. 31, 2018	$ 32	299,112	(162)	(200,689)	98,293
Shares, Outstanding, Beginning Balance at Mar. 31, 2018	31,888,998
Vesting of restricted stock		3			3
Vesting of restricted stock (in shares)	61,632
Exercises of vested stock options		1,116			1,116
Exercises of vested stock options (in shares)	113,318
Stock based compensation expense		8,065			8,065
Unrealized gain (loss) on available for-sale securities, net of tax			37		37
Net loss				(25,541)	(25,541)
Stockholders' Equity, Ending Balance at Jun. 30, 2018	$ 32	308,296	(125)	(226,230)	81,973
Shares, Outstanding, Ending Balance at Jun. 30, 2018	32,063,948
Vesting of restricted stock		2			2
Vesting of restricted stock (in shares)	110,750
Exercises of vested stock options		945			945
Exercises of vested stock options (in shares)	114,048
Issuance of common stock under ESPP		424			424
Issuance of common stock under ESPP (in shares)	20,954
Stock based compensation expense		2,583			2,583
Unrealized gain (loss) on available for-sale securities, net of tax			(49)		(49)
Net loss				(20,289)	(20,289)
Stockholders' Equity, Ending Balance at Sep. 30, 2018	$ 32	312,250	(174)	(246,519)	65,589
Shares, Outstanding, Ending Balance at Sep. 30, 2018	32,309,700
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 (loss) 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, 2018	$ 32	315,598	(133)	(269,051)	46,446
Shares, Outstanding, Beginning Balance at Dec. 31, 2018	32,364,895
Stockholders' Equity, Ending Balance at Jun. 30, 2019	$ 37	403,334	101	(285,068)	118,404
Shares, Outstanding, Ending Balance at Jun. 30, 2019	36,677,608
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 (in shares)					239,336
Unrealized gain (loss) on available for-sale securities, net of tax					$ 118
Net loss					(31,023)
Stockholders' Equity, Ending Balance at Sep. 30, 2019	$ 37	408,208	(15)	(300,074)	108,156
Shares, Outstanding, Ending Balance at Sep. 30, 2019	36,828,123
Stockholders' Equity, Beginning Balance at Mar. 31, 2019	$ 37	396,953	(75)	(296,221)	100,694
Shares, Outstanding, Beginning Balance at Mar. 31, 2019	36,575,983
Exercises of vested stock options		714			714
Exercises of vested stock options (in shares)	57,461
Issuance of common stock under ESPP		471			471
Issuance of common stock under ESPP (in shares)	44,164
Stock based compensation expense		5,196			5,196
Unrealized gain (loss) on available for-sale securities, net of tax			176		176
Net loss				11,153	11,153
Stockholders' Equity, Ending Balance at Jun. 30, 2019	$ 37	403,334	101	(285,068)	118,404
Shares, Outstanding, Ending Balance at Jun. 30, 2019	36,677,608
Exercises of vested stock options		1,608			1,608
Exercises of vested stock options (in shares)	150,515
Stock based compensation expense		3,266			3,266
Unrealized gain (loss) on available for-sale securities, net of tax			(116)		(116)
Net loss				(15,006)	(15,006)
Stockholders' Equity, Ending Balance at Sep. 30, 2019	$ 37	$ 408,208	$ (15)	$ (300,074)	$ 108,156
Shares, Outstanding, Ending Balance at Sep. 30, 2019	36,828,123