Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax, beginning of period	$ (169)	$ 53	$ 1,558	$ (2,493)
Other comprehensive income (loss) before reclassifications	(15,824)	1,546	(17,591)	4,479
Amount reclassified from accumulated other comprehensive income	(838)	(14)	(798)	(401)
Other comprehensive income (loss), net of tax	(16,662)	1,532	(18,389)	4,078
Accumulated other comprehensive income (loss), net of tax, end of period	(16,831)	1,585	(16,831)	1,585
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Net gain on securities transactions	1,432	55	1,434	732
Salaries and employee benefits	7,647	7,519	15,825	15,262
Income taxes	5,824	5,328	11,296	10,577
Net income	9,763	9,066	18,931	17,975
Reclassification Out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Net income	838	14	798	401
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	1,987	1,509	3,755	(1,018)
Other comprehensive income (loss) before reclassifications	(15,824)	1,546	(17,591)	4,479
Amount reclassified from accumulated other comprehensive income	(859)	(33)	(860)	(439)
Other comprehensive income (loss), net of tax	(16,683)	1,513	(18,451)	4,040
Accumulated other comprehensive income (loss), net of tax, end of period	(14,696)	3,022	(14,696)	3,022
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	1,432	55	1,434	732
Income taxes	(573)	(22)	(574)	(293)
Net income	859	33	860	439
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	(2,156)	(1,456)	(2,197)	(1,475)
Other comprehensive income (loss) before reclassifications	0	0	0	0
Amount reclassified from accumulated other comprehensive income	21	19	62	38
Other comprehensive income (loss), net of tax	21	19	62	38
Accumulated other comprehensive income (loss), net of tax, end of period	(2,135)	(1,437)	(2,135)	(1,437)
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	15	13	40	25
Net income	(21)	(19)	(62)	(38)
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	65	65	131	131
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	$ (101)	$ (97)	$ (233)	$ (194)