Earnings per Share (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
Earnings Per Share [Abstract]
Net income available to common shareholders	$ 22,751	$ 20,979	$ 44,370	$ 38,590
Undistributed Earnings (Loss) Allocated to Participating Securities, Basic	(197)	(211)	(382)	(377)
Distributed earnings allocated to common stock	8,615	7,039	17,231	14,077
Undistributed earnings allocated to common stock	13,939	13,729	26,757	24,136
Net earnings allocated to common shareholders	$ 22,554	$ 20,768	$ 43,988	$ 38,213
Average shares outstanding (in shares)	16,368	15,326	16,390	15,370
Effect of dilutive securities:
Employee stock awards (in shares)	18	19	18	20
Average common shares outstanding, diluted (in shares)	16,386	15,345	16,408	15,390
Basic earnings per common share (in dollars per share)	$ 1.38	$ 1.36	$ 2.68	$ 2.49
Diluted earnings per share (in dollars per share)	$ 1.38	$ 1.35	$ 2.68	$ 2.48