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, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Numerator:
Net income	$ 10,348	$ 13,826	$ 13,275	$ 10,575	$ 11,387	$ 11,777	$ 19,247	$ 12,605	$ 48,024	$ 55,016	$ 51,991
Denominator:
Denominator for basic earnings per share–weighted average common shares									25,038	24,919	24,505
Effect of dilutive stock options									51	93	239
Effect of other common stock equivalents									591	459	719
Denominator for diluted earnings per share–adjusted weighted average common shares									25,680	25,471	25,463
Basic Earnings Per Share	$ 0.41	$ 0.55	$ 0.53	$ 0.42	$ 0.46	$ 0.47	$ 0.77	$ 0.51	$ 1.92	$ 2.21	$ 2.12
Diluted Earnings Per Share	$ 0.40	$ 0.54	$ 0.52	$ 0.42	$ 0.45	$ 0.46	$ 0.75	$ 0.49	$ 1.87	$ 2.16	$ 2.04