Net Income per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share, Basic [Abstract]
Net income	$ 132,217	$ 142,943	$ 152,276
Average common shares outstanding (in shares)	32,334	34,179	34,306
Basic net income per common share (in dollars per share)	$ 4.09	$ 4.18	$ 4.44
Earnings Per Share, Diluted [Abstract]
Net income	$ 132,217	$ 142,943	$ 152,276
Average common shares outstanding (in shares)	32,334	34,179	34,306
Adjustment for common share equivalents (in shares)	28	32	137
Average common shares outstanding-diluted (in shares)	32,362	34,211	34,443
Diluted net income per common share (in dollars per share)	$ 4.09	$ 4.18	$ 4.42
Anti-dilutive shares (in shares)	26	2	0