Earnings Per Share - Computation of basic and diluted EPS (Details) - 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
Basic earnings per common share:
Net income	$ 51,565	$ 47,082	$ 137,392	$ 129,867
Weighted-average basic common shares	34,057	36,645	34,859	36,657
Basic earnings per common share (in dollars per share)	$ 1.51	$ 1.28	$ 3.94	$ 3.53
Diluted earnings per share:
Net income	$ 51,565	$ 47,082	$ 137,392	$ 129,867
Weighted-average basic common shares	34,057	36,645	34,859	36,657
Effect of dilutive securities (in shares)	243	248	210	252
Weighted-average dilutive shares	34,300	36,893	35,069	36,909
Diluted earnings per common share (in dollars per share)	$ 1.50	$ 1.28	$ 3.92	$ 3.52