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, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Numerator:
Net income	$ 79,709	$ 62,474	$ 37,291	$ 41,539	$ 28,454	$ 28,111	$ 179,474	$ 98,104
Denominator:
Denominator for basic earnings per share–weighted average common shares	26,334			26,150			26,317	26,118
Effect of dilutive stock options	109			109			113	96
Effect of other common stock equivalents	270			356			269	355
Denominator for diluted earnings per share–adjusted weighted average common shares	26,713			26,615			26,699	26,569
Basic Earnings Per Share	$ 3.03			$ 1.59			$ 6.82	$ 3.76
Diluted Earnings Per Share	$ 2.98			$ 1.56			$ 6.72	$ 3.69