Consolidated and Combined Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	February 2015	July 2015	Preferred Stock Series A Convertible Preferred Stock	Preferred Stock Series A 1 Convertible Preferred Stock	Preferred Stock Series B Convertible Preferred Stock	Common Stock	Common Stock February 2015	Common Stock July 2015	Additional Paid-in Capital	Additional Paid-in Capital February 2015	Additional Paid-in Capital July 2015	Receivables from Stockholder	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance at Dec. 31, 2013	$ (11,017)						$ 1			$ 2,200			$ (335)		$ (12,883)
Beginning balance, temporary equity at Dec. 31, 2013				$ 19,909	$ 2,768	$ 38,414
Beginning balance (in shares) at Dec. 31, 2013							12,004,000
Beginning balance, temporary equity (in shares) at Dec. 31, 2013				46,356,000	5,538,000	43,529,000
Issuance of common stock, net of discounts and offering costs, Value	56,456						$ 1			56,455
Issuance of common stock, net of discounts and offering costs, shares							5,750,000
Issuance of preferred stock						$ 13,481
Issuance of preferred stock, shares						15,263,000
Interest income accrued on notes receivable from stockholder	(2)												(2)
Repayment of notes receivable from stockholder	337												$ 337
Issuance of common stock upon vesting of restricted stock awards	20									20
Issuance of common stock upon vesting of restricted stock awards, shares							645,000
Recapitalization (Note 2)							$ (1)			1
Recapitalization, shares (Note 2)				(41,205,000)	(4,923,000)	(52,260,000)	(11,346,000)
Issuance of common stock upon vesting of stock awards—post Recapitalization	70									70
Issuance of common stock upon vesting of stock awards—post Recapitalization, shares							282,000
Issuance of common stock for research and development expenses related to technology licensing option	750									750
Issuance of common stock for research and development expenses related to technology licensing option, shares							60,000
Conversion of preferred stock	$ 74,573			$ (19,909)	$ (2,768)	$ (51,895)	$ 1			74,572
Conversion of preferred stock, shares				(5,151,000)	(615,000)	(6,532,000)	12,298,000
Issuance of common stock pursuant to stock option exercises, shares	0
Stock-based compensation expense	$ 10,101									10,101
Net loss	(28,006)														(28,006)
Unrealized gain (loss) on available-for-sale securities	(100)													$ (100)
Ending balance at Dec. 31, 2014	103,182						$ 2			144,169				(100)	(40,889)
Ending balance (in shares) at Dec. 31, 2014							19,693,000
Issuance of common stock, net of discounts and offering costs, Value		$ 69,487	$ 193,947					$ 1			$ 69,486	$ 193,947
Issuance of common stock, net of discounts and offering costs, shares								4,147,000	3,981,000
Issuance of common stock upon vesting of restricted stock awards	80									80
Issuance of common stock upon vesting of restricted stock awards, shares							287,000
RSU settlements, net of shares withheld	(4,647)									(4,647)
RSU settlements, net of shares withheld, shares							327,000
Issuance of common stock pursuant to stock option exercises	$ 439									439
Issuance of common stock pursuant to stock option exercises, shares	23,822						24,000
Stock-based compensation expense	$ 10,251									10,251
Net loss	(57,221)														(57,221)
Unrealized gain (loss) on available-for-sale securities	(418)													(418)
Ending balance at Dec. 31, 2015	315,100						$ 3			413,725				(518)	(98,110)
Ending balance (in shares) at Dec. 31, 2015							28,459,000
Issuance of common stock upon vesting of restricted stock awards	60									60
Issuance of common stock upon vesting of restricted stock awards, shares							233,000
RSU settlements, net of shares withheld	$ (94)									(94)
RSU settlements, net of shares withheld, shares							199,000
Issuance of common stock pursuant to stock option exercises, shares	18,947
Issuance of common stock pursuant to employee stock awards	$ 600									600
Issuance of common stock pursuant to employee stock awards, shares							42,000
Stock-based compensation expense	16,784									16,784
Net loss	(79,049)														(79,049)
Unrealized gain (loss) on available-for-sale securities	335													335
Ending balance at Dec. 31, 2016	$ 253,736						$ 3			$ 431,075				$ (183)	$ (177,159)
Ending balance (in shares) at Dec. 31, 2016							28,933,000