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, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator:
Net income	$ 47,759	$ 14,407	$ 17,603	$ 11,387	$ 10,348	$ 13,826	$ 13,275	$ 10,575	$ 91,156	$ 48,024	$ 55,016
Denominator:
Denominator for basic earnings per share–weighted average common shares									25,518	25,038	24,919
Effect of dilutive stock options and restricted stock									142	51	93
Effect of other common stock equivalents									426	591	459
Denominator for diluted earnings per share–adjusted weighted average common shares									26,086	25,680	25,471
Basic Earnings Per Share	$ 1.87	$ 0.56	$ 0.69	$ 0.45	$ 0.41	$ 0.55	$ 0.53	$ 0.42	$ 3.57	$ 1.92	$ 2.21
Diluted Earnings Per Share	$ 1.82	$ 0.55	$ 0.68	$ 0.44	$ 0.40	$ 0.54	$ 0.52	$ 0.42	$ 3.49	$ 1.87	$ 2.16