Net Income per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share, Basic [Abstract]
Net income	$ 41,346	$ 36,495	$ 93,325	$ 107,487
Average common shares outstanding (in shares)	32,229	34,233	32,434	34,418
Basic net income per common share (in dollars per share)	$ 1.28	$ 1.07	$ 2.88	$ 3.12
Earnings Per Share, Diluted [Abstract]
Net income	$ 41,346	$ 36,495	$ 93,325	$ 107,487
Average common shares outstanding (in shares)	32,229	34,233	32,434	34,418
Adjustment for common share equivalents (in shares)	22	23	24	33
Average common shares outstanding-diluted (in shares)	32,251	34,256	32,458	34,451
Diluted net income per common share (in dollars per share)	$ 1.28	$ 1.07	$ 2.88	$ 3.12
Anti-dilutive shares	26	2	26	20