Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	0	2
Net income available to common shareholders	$ 21,619	$ 17,616
Undistributed Earnings (Loss) Allocated to Participating Securities, Basic	(186)	(195)
Distributed earnings allocated to common stock	8,661	7,023
Undistributed earnings allocated to common stock	12,772	10,398
Net earnings allocated to common shareholders	$ 21,433	$ 17,421
Average shares outstanding (in shares)	16,411	15,414
Effect of dilutive securities:
Employee stock awards (in shares)	18	22
Average common shares outstanding, diluted (in shares)	16,429	15,436
Basic earnings per common share (in dollars per share)	$ 1.31	$ 1.13
Diluted earnings per share (in dollars per share)	$ 1.30	$ 1.13