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, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Number of Shares
Beginning Balance			3,481,469
Granted	116,000	1,800	136,000	51,800
Exercised			(169,000)
Cancelled			(10,366)
Ending Balance	3,438,103		3,438,103		3,481,469
Vested and unvested expected to vest at end of period	3,353,760		3,353,760
Options exercisable, at end of period	2,237,935		2,237,935		2,120,834
Options available for future grant	2,642,596		2,642,596
Weighted Average Exercise Price
Beginning Balance			$ 4.96
Granted			8.13
Exercised			4.81
Cancelled			6.48
Ending Balance	$ 5.08		5.08		$ 4.96
Vested and unvested expected to vest at end of period	5.08		5.08
Options exercisable, at end of period	$ 5.08		$ 5.08		$ 4.24
Weighted Average Contractual Term (Years)
Outstanding, at end of period			6 years 9 months
Vested and unvested expected to vest at end of period			5 years 8 months 16 days
Options exercisable, at end of period			5 years 8 months 16 days		5 years 10 months 2 days
Aggregate Intrinsic Value
Outstanding, at end of period	$ 4,046		$ 4,046
Vested and unvested expected to vest at end of period	3,947		3,947
Options exercisable, at end of period	$ 3,430		$ 3,430		$ 8,622