Stock Option Activity Under Stock Option Plan (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Number of Shares
Beginning Balance	6,505,663
Granted	50,000	80,500
Exercised	(592,200)
Cancelled	(39,166)
Ending Balance	5,924,297		6,505,663
Vested and unvested expected to vest at end of period	5,878,611
Options exercisable, at end of period	3,185,297		3,781,162
Options available for future grant	4,572,935
Weighted Average Exercise Price
Beginning Balance	$ 4.07
Granted	$ 9.10
Exercised	$ 4.29
Cancelled	$ 4.26
Ending Balance	$ 4.09		$ 4.07
Vested and unvested expected to vest at end of period	$ 4.08
Options exercisable, at end of period	$ 4.08		$ 4.10
Weighted Average Contractual Term (Years)
Outstanding, at end of period	6 years 4 months 10 days
Vested and unvested expected to vest at end of period	5 years 3 months 29 days
Options exercisable, at end of period	5 years 3 months 29 days		5 years 9 months 18 days
Aggregate Intrinsic Value
Outstanding, at end of period	$ 39,564
Vested and unvested expected to vest at end of period	39,259
Options exercisable, at end of period	$ 21,297		$ 4,130