Net Income Per Share - Schedule of Earnings Per Share, Basic and Diluted (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Numerator:
Net income, as reported	$ 7,039	$ 7,064	$ 23,175	$ 22,991
Less: net income attributable to participating securities	(140)	(114)	(430)	(383)
Net income available to common shareholders-basic and diluted	$ 6,899	$ 6,950	$ 22,745	$ 22,608
Basic:
Weighted-average shares of common stock outstanding	39,222,580	38,919,553	39,290,673	38,368,929
Less: weighted-average shares of unvested restricted common stock outstanding	(791,549)	(642,663)	(747,272)	(651,046)
Weighted-average number of common shares used in computing basic net income per common share	38,431,031	38,276,890	38,543,401	37,717,883
Net income per share applicable to common shareholders-basic	$ 0.18	$ 0.18	$ 0.59	$ 0.60
Diluted:
Weighted-average shares of common stock outstanding	39,222,580	38,919,553	39,290,673	38,368,929
Less: weighted-average shares of unvested restricted common stock outstanding	(791,549)	(642,663)	(747,272)	(651,046)
Weighted-average number of common shares issuable upon exercise of outstanding stock options, based on the treasury stock method	893,081	1,164,688	946,674	1,283,758
Weighted-average number of restricted stock outstanding, based on the treasury stock method	163,190	215,896	173,732	204,274
Weighted-average number of common shares used in computing diluted net income per common share	39,487,302	39,657,474	39,663,807	39,205,915
Net income per share applicable to common shareholders-diluted	$ 0.17	$ 0.18	$ 0.57	$ 0.58