Shareholders' Equity - Schedule of Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Calculation of Earnings per share
Net income available to common equity	$ 39,796	$ 38,766	$ 39,135
Average common shares outstanding - basic (in shares)	26,602	25,497	22,137
Dilutive stock options and warrants (in shares)	120	317	1,726
Average common shares outstanding - dilutive (in shares)	26,722	25,814	23,863
Earnings per share - basic (in dollars per share)	$ 1.50	$ 1.52	$ 1.77
Earnings per share - dilutive (in dollars per share)	$ 1.49	$ 1.50	$ 1.64