Earnings Per Share - Computation of basic and diluted EPS (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Basic earnings per common share:
Net income	$ 41,460	$ 40,459	$ 85,827	$ 82,785
Weighted-average basic common shares	35,089	36,677	35,268	36,657
Basic earnings per common share (in dollars per share)	$ 1.18	$ 1.10	$ 2.43	$ 2.25
Diluted earnings per share:
Net income	$ 41,460	$ 40,459	$ 85,827	$ 82,785
Weighted-average basic common shares	35,089	36,677	35,268	36,657
Effect of dilutive securities (in shares)	211	252	193	253
Weighted-average dilutive shares	35,300	36,929	35,461	36,910
Diluted earnings per common share (in dollars per share)	$ 1.17	$ 1.09	$ 2.42	$ 2.24