Stock Option Activity Under Stock Option Plan (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Number of Shares
Beginning Balance			6,505,663
Granted	1,800	23,800	51,800	104,300
Exercised			(2,860,299)
Cancelled			(153,833)
Ending Balance	3,543,331		3,543,331		6,505,663
Vested and unvested expected to vest at end of period	3,491,349		3,491,349
Options exercisable, at end of period	1,912,531		1,912,531		3,781,162
Options available for future grant	3,635,802		3,635,802
Weighted Average Exercise Price
Beginning Balance			$ 4.07
Granted			9.11
Exercised			3.97
Cancelled			4.13
Ending Balance	$ 4.23		4.23		$ 4.07
Vested and unvested expected to vest at end of period	4.12		4.12
Options exercisable, at end of period	$ 4.12		$ 4.12		$ 4.10
Weighted Average Contractual Term (Years)
Outstanding, at end of period			3 years 10 months 21 days
Vested and unvested expected to vest at end of period			5 years 9 months 4 days
Options exercisable, at end of period			5 years 9 months 4 days		5 years 9 months 18 days
Aggregate Intrinsic Value
Outstanding, at end of period	$ 27,534		$ 27,534
Vested and unvested expected to vest at end of period	27,130		27,130
Options exercisable, at end of period	$ 15,074		$ 15,074		$ 4,130