Common and Convertible Preferred Stock - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands			9 Months Ended
	Apr. 20, 2015	Feb. 02, 2015	Sep. 30, 2015	Sep. 30, 2014	Oct. 27, 2015	Dec. 31, 2014
Class of Stock [Line Items]
Convertible preferred stock issued			44,683,824			10,000,000
Convertible preferred stock, par value			$ 0.0001			$ 0.0001
Proceeds from issuance of convertible preferred stock, gross			$ 79,219	$ 4,875
Stock issuance costs for convertible preferred stock			$ 1,501
Common stock, shares authorized			68,000,000			65,700,000
Common stock, par value			$ 0.0001			$ 0.0001
Undesignated preferred stock, shares authorized			44,683,824			45,000,000
Series A Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Convertible preferred stock issued		14,500,000
Shares issued, price per share		$ 1.00
Convertible preferred stock, par value		$ 0.0001
Proceeds from issuance of convertible preferred stock, gross		$ 14,500
Stock issuance costs for convertible preferred stock		$ 20
Series B Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Convertible preferred stock issued	20,183,824
Shares issued, price per share	$ 3.2204
Convertible preferred stock, par value	$ 0.0001
Proceeds from issuance of convertible preferred stock, gross	$ 65,000
Stock issuance costs for convertible preferred stock	$ 261
Subsequent Event [Member]
Class of Stock [Line Items]
Convertible preferred stock, par value					$ 0.0001
Common stock, shares authorized					150,000,000
Common stock, par value					$ 0.0001
Undesignated preferred stock, shares authorized					5,000,000