Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Basic and Diluted Earnings Per Share
Net income available to common stockholders, basic and diluted	$ 36,479	$ 30,957	$ 101,421	$ 90,090
Average outstanding shares - basic	78,004,450	76,288,640	77,379,514	76,195,550
Add: dilutive restricted stock awards	61,492	62,233	63,430	51,501
Average outstanding shares - diluted	78,065,942	76,350,873	77,442,944	76,247,051
Basic earnings per share	$ 0.47	$ 0.40	$ 1.31	$ 1.18
Diluted earnings per share	$ 0.47	$ 0.40	$ 1.31	$ 1.18
Earnings Per Share
Restricted stock awards excluded from the diluted average outstanding share calculation			0	10,677