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								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Numerator:
Net income, as reported	$ 8,094	$ 7,064	$ 7,311	$ 8,616	$ 7,840	$ 7,990	$ 7,415	$ 5,720	$ 31,085	$ 28,965	$ 22,669
Less: net income attributable to participating securities									(503)	(469)	(367)
Net income available to common shareholders-basic and diluted for 2013, basic for 2012, basic and diluted for 2011	7,973	6,950	7,182	8,478	7,717	7,857	7,286	5,633	30,582	28,496	22,302
Basic:
Weighted-average shares of common stock outstanding									38,470,376	36,914,163	35,939,104
Less: weighted-average shares of unvested restricted common stock outstanding									(636,559)	(602,328)	(581,474)
Weighted-average number of common shares used in computing basic net income per common share									37,833,817	36,311,835	35,357,630
Net income per share applicable to common shareholders-basic	$ 0.21	$ 0.18	$ 0.19	$ 0.23	$ 0.21	$ 0.22	$ 0.20	$ 0.16	$ 0.81	$ 0.78	$ 0.63
Weighted-average shares of common stock outstanding									38,470,376	36,914,163	35,939,104
Less: weighted-average shares of unvested restricted common stock outstanding									(636,559)	(602,328)	(581,474)
Weighted-average number of common shares issuable upon exercise of outstanding stock options, based on the treasury stock method									1,240,629	1,250,118	1,326,873
Weighted-average number of shares of restricted common stock outstanding, based on the treasury stock method									211,205		132,876
Weighted-average number of common shares used in computing diluted net income per common share									39,285,651	37,561,953	36,817,379
Net income per share applicable to common shareholders-diluted	$ 0.20	$ 0.18	$ 0.18	$ 0.22	$ 0.20	$ 0.21	$ 0.19	$ 0.15	$ 0.78	$ 0.76	$ 0.61
Net income available to common shareholders-basic	7,973	6,950	7,182	8,478	7,717	7,857	7,286	5,633	30,582	28,496	22,302
Plus: undistributed earnings allocated to participating securities										424
Less: undistributed earnings reallocated to participating securities										(410)
Net income available to common shareholders-diluted	$ 7,973	$ 6,950	$ 7,185	$ 8,481	$ 7,720	$ 7,857	$ 7,286	$ 5,636	$ 30,582	$ 28,510	$ 22,302
Weighted-average shares of common stock outstanding									38,470,376	36,914,163	35,939,104
Less: weighted-average shares of unvested restricted common stock outstanding									(636,559)	(602,328)	(581,474)
Weighted-average number of common shares issuable upon exercise of outstanding stock options, based on the treasury stock method									1,240,629	1,250,118	1,326,873
Weighted-average number of common shares used in computing diluted net income per common share									39,285,651	37,561,953	36,817,379
Net income per share applicable to common shareholders-diluted	$ 0.20	$ 0.18	$ 0.18	$ 0.22	$ 0.20	$ 0.21	$ 0.19	$ 0.15	$ 0.78	$ 0.76	$ 0.61