Preferred Stock Warrants - Additional Information (Detail) - USD ($)		3 Months Ended	9 Months Ended
	Jul. 21, 2015	Sep. 30, 2015	Sep. 30, 2015	Dec. 31, 2014
Class of Warrant or Right [Line Items]
Estimated fair value of warrant		$ 0.0	$ 0.0	$ 1,800,000
Fair value of warrant liability reclassified to redeemable convertible preferred stock and additional paid-in capital		18,200,000	19,253,000
Warrants exercised	493,648
Warrants exercise price	$ 17.00
Cash proceeds from warrants exercised		$ 1,200,000	$ 1,500,000
Number of common stock shares issued upon exercise of preferred stock warrants	390,680	481,671	481,671
Series B Redeemable Convertible Preferred Stock [Member]
Class of Warrant or Right [Line Items]
Warrants exercised	10,414
Number of common stock shares issued upon exercise of preferred stock warrants	6,499
Series B-1 Redeemable Convertible Preferred Stock [Member]
Class of Warrant or Right [Line Items]
Warrants exercised	349,054
Number of common stock shares issued upon exercise of preferred stock warrants	291,164	444,286	444,286
Series C Redeemable Convertible Preferred Stock [Member]
Class of Warrant or Right [Line Items]
Warrants exercised	134,180
Number of common stock shares issued upon exercise of preferred stock warrants	93,017	37,385	37,385
Series B-1 Redeemable Convertible Preferred Stock Cash Exercised at Exercise Price of $7.45 [Member]
Class of Warrant or Right [Line Items]
Warrants exercised		28,699	31,778
Warrants exercise price		$ 7.45	$ 7.45
Series B-1 Redeemable Convertible Preferred Stock Warrants Cash Exercised at Exercise Price of $2.6075 [Member]
Class of Warrant or Right [Line Items]
Warrants exercised		329,559	412,508
Warrants exercise price		$ 2.6075	$ 2.6075
Series C Redeemable Convertible Preferred Stock Warrants Cash Exercised at Exercise Price of $5.215 [Member]
Class of Warrant or Right [Line Items]
Warrants exercised		32,138	37,385
Warrants exercise price		$ 5.215	$ 5.215