Income Taxes Income Tax Reconciliation (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
Effective Income Tax Rate [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate									35.00%
Expected income taxes									$ 9,006	$ 8,650	$ 8,249
Tax-exempt income									(1,103)	(954)	(877)
Nondeductible interest expense									11	10	9
State taxes, net of federal taxes									1,264	1,505	1,429
Other items									41	43	36
Effect of marginal tax rate									(1)	0	0
Total	$ 2,584	$ 1,979	$ 2,352	$ 2,303	$ 2,330	$ 2,355	$ 2,431	$ 2,138	$ 9,218	$ 9,254	$ 8,846