Computation of Earnings Per Share - Summary of Calculation of Basic Earnings Per Common Share and Diluted Earnings Per Common Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Numerator:
Net income	$ 12,908	$ 9,256	$ 35,563	$ 26,642
Denominator:
Denominator for basic earnings per share-weighted average common shares	24,220	23,850	24,123	23,810
Effect of dilutive stock options	286	203	300	171
Effect of other common stock equivalents	763	810	750	813
Denominator for diluted earnings per share-adjusted weighted average common shares	25,269	24,863	25,173	24,794
Basic Earnings Per Share	$ 0.53	$ 0.39	$ 1.47	$ 1.12
Diluted Earnings Per Share	$ 0.51	$ 0.37	$ 1.41	$ 1.07