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, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Numerator:
Net income	$ 41,539	$ 28,454	$ 28,111	$ 32,968	$ 37,073	$ 22,259	$ 98,104	$ 92,300
Denominator:
Denominator for basic earnings per share–weighted average common shares	26,150			25,978			26,118	25,936
Effect of dilutive stock options	109			125			96	120
Effect of other common stock equivalents	356			357			355	357
Denominator for diluted earnings per share–adjusted weighted average common shares	26,615			26,460			26,569	26,413
Basic Earnings Per Share	$ 1.59			$ 1.27			$ 3.76	$ 3.56
Diluted Earnings Per Share	$ 1.56			$ 1.25			$ 3.69	$ 3.49