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						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Numerator:
Net income	$ 32,968	$ 37,073	$ 22,259	$ 28,195	$ 30,281	$ 21,125	$ 92,300	$ 79,601
Denominator:
Denominator for basic earnings per share–weighted average common shares	25,978			25,792			25,936	25,752
Effect of dilutive stock options	125			167			120	168
Effect of other common stock equivalents	357			395			357	408
Denominator for diluted earnings per share–adjusted weighted average common shares	26,460			26,354			26,413	26,328
Basic Earnings Per Share	$ 1.27			$ 1.09			$ 3.56	$ 3.09
Diluted Earnings Per Share	$ 1.25			$ 1.07			$ 3.49	$ 3.02