Common Stock - Additional Information (Details) - USD ($)		1 Months Ended	12 Months Ended
	Apr. 20, 2015	May 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Class Of Stock [Line Items]
Preferred stock shares authorized	10,000,000		10,000,000	10,000,000
Common stock shares authorized	300,000,000		300,000,000	300,000,000
Net proceeds from issuance of common stock, after deducting commissions and expenses payable			$ 36,806,000	$ 150,283,000
IPO
Class Of Stock [Line Items]
Issuance of common stock				124,193,000
Private Placement
Class Of Stock [Line Items]
Issuance of common stock				$ 25,000,000
At-the-Market Offering | Sales Agreement | Cowen and Company, LLC
Class Of Stock [Line Items]
Issuance of common stock (in shares)			2,526,229
Commission on sales of common stock, percentage		3.00%
Net proceeds from issuance of common stock, after deducting commissions and expenses payable			$ 36,800,000
Aggregate offering available for issuance of common stock			$ 63,200,000
At-the-Market Offering | Sales Agreement | Cowen and Company, LLC | Maximum
Class Of Stock [Line Items]
Aggregate offering from offer and sell of common stock		$ 100,000,000
Common Stock
Class Of Stock [Line Items]
Number of common stock issued on conversion of convertible preferred stock				51,822,659
Common Stock | IPO
Class Of Stock [Line Items]
Issuance of common stock (in shares)	8,050,000			8,050,000
Stock price per share	$ 17.00
Proceeds from IPO net of underwriting discount, commission and offering expenses	$ 124,200,000
Issuance of common stock				$ 1,000
Number of common stock issued on conversion of convertible preferred stock	51,822,659
Common Stock | Exercise of Underwriters
Class Of Stock [Line Items]
Issuance of common stock (in shares)	1,050,000
Common Stock | Private Placement
Class Of Stock [Line Items]
Issuance of common stock (in shares)				1,470,588
Novartis Agreement | Common Stock | Private Placement
Class Of Stock [Line Items]
Issuance of common stock (in shares)	1,470,588
Stock price per share	$ 17.00
Issuance of common stock	$ 25,000,000