Preferred Stock Warrants - Summary of Redeemable Convertible Preferred Stock Warrants (Detail) - $ / shares	6 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Class of Warrant or Right [Line Items]
Warrants Outstanding	884,044	975,335
Series B Preferred Stock Warrants [Member]
Class of Warrant or Right [Line Items]
Warrants Outstanding	10,414	10,414
Warrants Outstanding, Exercise Price	$ 7.4500
Warrants Outstanding, Expiration Description	July 31, 2018
Series B-1 Preferred Stock Warrants, Expiration June 30, 2018 [Member]
Class of Warrant or Right [Line Items]
Warrants Outstanding	43,969	47,060
Warrants Outstanding, Exercise Price	$ 7.4500
Warrants Outstanding, Expiration Description	June 30, 2018
Series B-1 Preferred Stock Warrants, Expiration Various Dates In 2016 - 2021 [Member]
Class of Warrant or Right [Line Items]
Warrants Outstanding	663,343	746,295
Warrants Outstanding, Exercise Price	$ 2.6075
Warrants Outstanding, Expiration Description	Various dates in 2016 - 2021
Series C Preferred Stock Warrants [Member]
Class of Warrant or Right [Line Items]
Warrants Outstanding	166,318	171,566
Warrants Outstanding, Exercise Price	$ 5.2150
Warrants Outstanding, Expiration Description	Various dates in 2022 - 2023