Net Income per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Earnings Per Share, Basic [Abstract]
Net income	$ 47,993	$ 28,856	$ 91,462	$ 51,979
Average common shares outstanding (in shares)	31,963	32,225	31,916	32,537
Basic net income per common share (in dollars per share)	$ 1.50	$ 0.90	$ 2.87	$ 1.60
Earnings Per Share, Diluted [Abstract]
Net income	$ 47,993	$ 28,856	$ 91,462	$ 51,979
Average common shares outstanding (in shares)	31,963	32,225	31,916	32,537
Adjustment for common share equivalents (in shares)	62	16	58	24
Average common shares outstanding-diluted (in shares)	32,025	32,241	31,974	32,561
Diluted net income per common share (in dollars per share)	$ 1.50	$ 0.90	$ 2.86	$ 1.60
Anti-dilutive shares (in shares)	3	49	3	26