Nature of Business - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	Sep. 22, 2015	Sep. 30, 2016	Dec. 31, 2015
Class of Stock [Line Items]
Accumulated deficit		$ (94,979)	$ (51,620)
Cash, cash equivalents and marketable securities		$ 184,857
Common Stock [Member]
Class of Stock [Line Items]
Conversion of convertible preferred stock into common stock upon initial public offering, Shares	16,298
Initial Public Offering [Member]
Class of Stock [Line Items]
Issuance of convertible preferred stock, shares	7,245
Stock issuance price per share	$ 22.00
Initial Public Offering [Member] | Common Stock [Member]
Class of Stock [Line Items]
Net proceeds from issuance of common stock	$ 145,184
Overallotment Option [Member]
Class of Stock [Line Items]
Issuance of convertible preferred stock, shares	945