Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax, beginning of period	$ 1,558	$ (2,493)
Other comprehensive income (loss) before reclassifications	(1,767)	2,967
Amount reclassified from accumulated other comprehensive income	40	(421)
Other comprehensive income (loss)	(1,727)	2,546
Accumulated other comprehensive income (loss), net of tax, end of period	(169)	53
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Net gain on securities transactions	2	677
Salaries and employee benefits	8,178	7,743
Income taxes	5,472	5,249
Net income	9,168	8,909
Reclassification Out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Net income	(40)	421
Unrealized Gain (Losses) on Securities Available For Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax, beginning of period	3,755	(1,018)
Other comprehensive income (loss) before reclassifications	(1,767)	2,967
Amount reclassified from accumulated other comprehensive income	(1)	(440)
Other comprehensive income (loss)	(1,768)	2,527
Accumulated other comprehensive income (loss), net of tax, end of period	1,987	1,509
Unrealized Gain (Losses) on Securities Available For Sale [Member] | Reclassification Out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Net gain on securities transactions	2	677
Income taxes	(1)	(237)
Net income	1	440
Net Change in Net Actuarial Loss and Prior Service Credit on Pension and Postretirement Benefit Plans, Net of Tax [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax, beginning of period	(2,197)	(1,475)
Other comprehensive income (loss) before reclassifications	0	0
Amount reclassified from accumulated other comprehensive income	41	19
Other comprehensive income (loss)	41	19
Accumulated other comprehensive income (loss), net of tax, end of period	(2,156)	(1,456)
Net Change in Net Actuarial Loss and Prior Service Credit on Pension and Postretirement Benefit Plans, Net of Tax [Member] | Reclassification Out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Income taxes	25	12
Net income	(41)	(19)
Amortization Of Prior Service Cost [Member] | Reclassification Out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Salaries and employee benefits	66	66
Amortization of Net Actuarial Loss [Member] | Reclassification Out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Salaries and employee benefits	$ (132)	$ (97)