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		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Numerator:
Net income, as reported	$ 7,311	$ 7,415	$ 15,927	$ 13,135
Less: net income attributable to participating securities	(129)	(129)	(269)	(214)
Net income available to common shareholders-basic	7,182	7,286	15,658	12,921
Add-back: undistributed earnings allocated to unvested shareholders	91		195
Less: undistributed earnings reallocated to unvested shareholders	(88)		(188)
Net income available to common shareholders-diluted	$ 7,185	$ 7,286	$ 15,665	$ 12,921
Diluted:
Weighted-average shares of common stock outstanding	38,420,617	36,689,475	38,070,822	36,764,611
Less: weighted-average shares of unvested restricted common stock outstanding	(695,535)	(642,750)	(655,308)	(600,044)
Weighted-average number of common shares issuable upon exercise of outstanding stock options, based on the treasury stock method	1,304,571	1,263,738	1,343,293	1,294,178
Weighted-average number of restricted stock, based on the treasury stock method		113,069		131,212
Weighted-average number of common shares used in computing diluted net income per common share	39,029,653	37,423,532	38,758,807	37,589,957
Net income per share applicable to common shareholders-diluted	$ 0.18	$ 0.19	$ 0.40	$ 0.34
Basic:
Weighted-average shares of common stock outstanding	38,420,617	36,689,475	38,070,822	36,764,611
Less: weighted-average shares of unvested restricted common stock outstanding	(695,535)	(642,750)	(655,308)	(600,044)
Weighted-average number of common shares used in computing basic net income per common share	37,725,082	36,046,725	37,415,514	36,164,567
Net income per share applicable to common shareholders-basic	$ 0.19	$ 0.20	$ 0.42	$ 0.36