Earnings per 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 [Abstract]
Net income available to common shareholders	$ 20,126	$ 22,371	$ 67,374	$ 66,741
Less: earnings allocated to participating securities	(198)	(192)	(658)	(567)
Net earnings allocated to common shareholders	19,928	22,179	66,716	66,174
Distributed earnings allocated to common stock	8,944	9,213	26,832	26,346
Undistributed earnings allocated to common stock	$ 10,984	$ 12,966	$ 39,884	$ 39,828
Average shares outstanding (in shares)	15,950	16,271	16,065	16,350
Effect of dilutive securities:
Employee stock awards (in shares)	20	18	19	18
Average common shares outstanding, diluted (in shares)	15,970	16,289	16,084	16,368
Basic earnings per common share (in dollars per share)	$ 1.25	$ 1.36	$ 4.15	$ 4.05
Diluted earnings per share (in dollars per share)	$ 1.25	$ 1.36	$ 4.15	$ 4.04