Computation of Earnings Per Share - Summary of Calculation of Basic Earnings Per Common Share and Diluted Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Numerator:
Net income	$ 11,387	$ 11,777	$ 19,247	$ 12,605	$ 13,569	$ 16,278	$ 13,568	$ 8,576	$ 55,016	$ 51,991	$ 43,627
Denominator:
Denominator for basic earnings per share–weighted average common shares									24,919	24,505	24,154
Effect of dilutive stock options									93	239	297
Effect of other common stock equivalents									459	719	754
Denominator for diluted earnings per share–adjusted weighted average common shares									25,471	25,463	25,205
Basic Earnings Per Share	$ 0.46	$ 0.47	$ 0.77	$ 0.51	$ 0.55	$ 0.66	$ 0.55	$ 0.35	$ 2.21	$ 2.12	$ 1.81
Diluted Earnings Per Share	$ 0.46	$ 0.46	$ 0.75	$ 0.49	$ 0.53	$ 0.64	$ 0.53	$ 0.34	$ 2.16	$ 2.04	$ 1.73