Earnings Per Share - Computation of Basic Earnings and Diluted Earnings Per Share Data (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Numerator for basic and diluted earnings per share:
Net income	$ 46,790	$ 40,390	$ 31,999	$ 27,348	$ 31,552	$ 38,924	$ 39,161	$ 37,825	$ 146,527	$ 147,462	$ 169,571
Denominator:
Weighted-average basic common shares outstanding									38,640	38,445	37,273
Assumed conversion of dilutive securities:
Stock options (in shares)									1,465	1,678	1,973
Denominator for diluted earnings per share - Adjusted weighted-average shares	40,736	40,280	39,813	39,585	39,891	40,528	40,224	39,836	40,105	40,123	39,246
Earnings per common share:
Basic (USD per share)									$ 3.79	$ 3.84	$ 4.55
Diluted (USD per share)	$ 1.15	$ 1.00	$ 0.80	$ 0.69	$ 0.79	$ 0.96	$ 0.97	$ 0.95	$ 3.65	$ 3.68	$ 4.32