Income Tax - Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Currently Payable:
Federal									$ 18,998	$ 21,221	$ 7,075
Deferred:
Federal									8,233	3,952	14,538
State									378	492	510
Income Tax Expense	$ 7,850	$ 7,469	$ 6,716	$ 5,574	$ 4,418	$ 6,557	$ 8,856	$ 5,834	$ 27,609	$ 25,665	$ 22,123