Share-Based Payments - Summary of Stock Option Activity and Related Information (Detail) - $ / shares	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Shares
Outstanding at beginning of period	1,438,528
Granted	799,828
Exercised	(75,549)
Cancelled or forfeited	(230,318)
Outstanding at end of period	1,932,489	1,438,528
Exercisable at September 30, 2015	828,209
Vested and expected to vest at September 30, 2015	1,637,621
Weighted-Average Exercise Price
Outstanding at beginning of period (in USD per share)	$ 4.93
Granted (in USD per share)	8.69
Exercised (in USD per share)	0.77
Cancelled or forfeited (in USD per share)	8.79
Outstanding at end of period (in USD per share)	6.19	$ 4.93
Exercisable at end of period (in USD per share)	4.96
Vested and expected to vest at end of period	$ 6.67
Remaining Contractual Life (in years)
Outstanding at beginning of period	7 years 10 months 28 days	7 years 10 months 10 days
Exercisable at September 30, 2015	7 years 3 months 11 days
Vested and expected to vest at September 30, 2015	8 years 1 month 17 days