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		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Numerator for basic and diluted earnings per share:
Net income	$ 40,390	$ 38,924	$ 99,737	$ 115,910
Denominator:
Weighted-average basic common shares outstanding (in shares)	38,765	38,761	38,614	38,533
Assumed conversion of dilutive securities:
Stock awards (in shares)	1,515	1,767	1,401	1,812
Denominator for diluted earnings per share - Adjusted weighted-average shares (in shares)	40,280	40,528	40,015	40,345
Earnings per common share:
Basic (usd per share)	$ 1.04	$ 1.00	$ 2.58	$ 3.01
Diluted (usd per share)	$ 1.00	$ 0.96	$ 2.49	$ 2.87