Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Net income available to common shareholders	$ 22,371	$ 20,692	$ 66,741	$ 59,283
Undistributed Earnings (Loss) Allocated to Participating Securities, Basic	(192)	(201)	(567)	(575)
Distributed earnings allocated to common stock	9,213	8,109	26,346	22,186
Undistributed earnings allocated to common stock	12,966	12,382	39,828	36,522
Net earnings allocated to common shareholders	$ 22,179	$ 20,491	$ 66,174	$ 58,708
Average shares outstanding (in shares)	16,271	15,340	16,350	15,360
Effect of dilutive securities:
Employee stock awards (in shares)	18	18	18	20
Average common shares outstanding, diluted (in shares)	16,289	15,358	16,368	15,380
Basic earnings per common share (in dollars per share)	$ 1.36	$ 1.34	$ 4.05	$ 3.82
Diluted earnings per share (in dollars per share)	$ 1.36	$ 1.33	$ 4.04	$ 3.82