Income Tax - Reconciliation of Income Tax Expense (Benefit) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Currently Payable:
Federal									$ 21,221	$ 7,075	$ 13,737
Deferred:
Federal									3,952	14,538	$ 2,147
State									492	510
Total Income Tax Expense	$ 4,418	$ 6,557	$ 8,856	$ 5,834	$ 5,638	$ 5,980	$ 5,888	$ 4,617	25,665	22,123	$ 15,884
Reconciliation of Federal Statutory to Actual Tax Expense:
Federal Statutory Income Tax at 35%									31,867	28,800	21,145
Tax-exempt Interest Income									(7,083)	$ (5,148)	$ (3,923)
Basis Difference on Sale of Insurance Subsidiary									2,252
Stock Compensation									34	$ 36	$ 50
Earnings on Life Insurance									(1,012)	(1,271)	(905)
Tax Credits									(583)	(911)	(857)
Other									190	617	374
Total Income Tax Expense	$ 4,418	$ 6,557	$ 8,856	$ 5,834	$ 5,638	$ 5,980	$ 5,888	$ 4,617	$ 25,665	$ 22,123	$ 15,884
Federal statutory income tax rate									35.00%	35.00%	35.00%