Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Novartis [Member] Collaborative Arrangement [Member]	Common Units [Member]	Common Stock [Member]	Incentive [Member]	Additional Paid-In Capital [Member]	Accumulated Deficit [Member]	Series A-1, Series A-2 and Junior Preferred [Member] Junior Preferred Units [Member]	Series A-1, Series A-2 and Junior Preferred [Member] Junior Preferred Units [Member] Novartis [Member] Collaborative Arrangement [Member]	Convertible Preferred Stock (Series B, Series A-2, Series A-1, Junior and Founder) [Member]	Class A-2 Preferred Units [Member]	Series B Preferred Stock [Member]
Beginning balance at Dec. 31, 2014	$ 7,566		$ 607		$ 50		$ (9,539)	$ 16,448
Beginning balance, shares at Dec. 31, 2014			2,298,000		1,558,498			19,348,694
Issuance of units/stock	1,984										$ 1,984
Issuance of units/stock, shares											1,333,333
Allocation from Novartis collaboration to carrying value of Preferred Shares	2,600	$ 2,644							$ 2,644
Tax provision associated with intraperiod tax allocation	(1,012)							$ (1,012)
Effect of Reorganization	(20,671)		$ (607)		$ (50)	$ 50		$ (20,064)		$ 20,671
Effect of Reorganization, shares			(2,298,000)	1,713,104	(1,558,498)			(20,682,027)		22,980,027
Issuance of Series B Preferred Shares, net of issuance costs												$ 67,263
Issuance of Series B Preferred Shares, net of issuance costs, shares												13,336,601
Equity-based compensation	685					685				$ 623
Equity-based compensation, shares				845,651
Net loss	(12,397)						(12,397)
Ending balance at Dec. 31, 2015										$ 88,557
Ending balance at Dec. 31, 2015	(21,201)					735	(21,936)
Ending balance, shares at Dec. 31, 2015				2,558,755
Ending balance, shares at Dec. 31, 2015										36,316,628
Conversion of convertible preferred stock	88,557			$ 3		88,554				$ (88,557)
Conversion of convertible preferred stock, shares				23,481,956						(36,316,628)
Issuance of units/stock	167,139			$ 1		167,138
Issuance of units/stock, shares				9,955,554
Exercise of stock options	2					2
Exercise of stock options, shares				257
Issuance of shares under employee stock purchase plan	259					259
Issuance of shares under employee stock purchase plan, shares				23,209
Equity-based compensation	6,715					6,715
Equity-based compensation, shares				(1,191)
Net loss	(31,634)						(31,634)
Ending balance at Dec. 31, 2016	$ 209,837			$ 4		263,403	(53,570)
Ending balance, shares at Dec. 31, 2016	36,018,540			36,018,540
Issuance of units/stock	$ 141,000					141,000
Issuance of units/stock, shares				6,250,000
Exercise of stock options	$ 1,156					1,156
Exercise of stock options, shares	141,759			141,759
Issuance of shares under employee stock purchase plan	$ 825					825
Issuance of shares under employee stock purchase plan, shares				64,786
Equity-based compensation	15,322					15,322
Equity-based compensation, shares				(90,462)
Net loss	(67,543)						(67,543)
Ending balance at Dec. 31, 2017	$ 300,597			$ 4		$ 421,706	$ (121,113)
Ending balance, shares at Dec. 31, 2017	42,384,623			42,384,623