Stock Option Activity Under Stock Option Plan (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Number of Shares
Beginning Balance			6,505,663
Granted	203,000	10,000	254,800	114,300
Exercised			(2,938,161)
Cancelled			(167,167)
Ending Balance	3,655,135		3,655,135		6,505,663
Vested and unvested expected to vest at end of period	3,579,108		3,579,108
Options exercisable, at end of period	1,886,001		1,886,001		3,781,162
Options available for future grant	3,441,950		3,441,950
Weighted Average Exercise Price
Beginning Balance			$ 4.07
Granted			11.61
Exercised			3.96
Cancelled			4.13
Ending Balance	$ 4.69		4.69		$ 4.07
Vested and unvested expected to vest at end of period	4.09		4.09
Options exercisable, at end of period	$ 4.09		$ 4.09		$ 4.10
Weighted Average Contractual Term (Years)
Outstanding, at end of period			7 years 1 month 2 days
Vested and unvested expected to vest at end of period			5 years 7 months 2 days
Options exercisable, at end of period			5 years 7 months 2 days		5 years 9 months 18 days
Aggregate Intrinsic Value
Outstanding, at end of period	$ 16,481		$ 16,481
Vested and unvested expected to vest at end of period	16,139		16,139
Options exercisable, at end of period	$ 9,277		$ 9,277		$ 4,130