Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Basic and Diluted Earnings Per Share
Net Income	$ 49,599	$ 49,336	$ 44,384	$ 38,559	$ 14,956	$ 36,479	$ 33,687	$ 31,255	$ 181,878	$ 116,377	$ 121,131
Average outstanding shares - basic									83,603,515	77,537,664	76,278,463
Add: dilutive restricted stock awards and stock options									73,670	69,941	63,373
Average outstanding shares - diluted									83,677,185	77,607,605	76,341,836
Basic earnings per share	$ 0.59	$ 0.58	$ 0.53	$ 0.48	$ 0.19	$ 0.47	$ 0.43	$ 0.41	$ 2.18	$ 1.50	$ 1.59
Diluted earnings per share	$ 0.59	$ 0.58	$ 0.52	$ 0.48	$ 0.19	$ 0.47	$ 0.43	$ 0.41	$ 2.17	$ 1.50	$ 1.59
Earnings Per Share
Restricted stock awards and stock options excluded from the diluted average outstanding share calculation									1,357	0	0