Income Taxes Income Tax Reconciliation (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Effective Income Tax Rate [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate									35.00%
Expected income taxes									$ 8,650	$ 8,249	$ 7,852
Tax-exempt income									(954)	(877)	(761)
Nondeductible interest expense									10	9	14
State taxes, net of federal taxes									1,505	1,429	1,264
Other items									43	36	41
Total	$ 2,330	$ 2,355	$ 2,431	$ 2,138	$ 2,140	$ 2,352	$ 2,220	$ 2,134	$ 9,254	$ 8,846	$ 8,410