Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax, beginning of period	$ (16,831)	$ 1,585	$ 1,558	$ (2,493)
Other comprehensive income (loss)- before reclassifications	878	3,675	(16,713)	8,154
Amount reclassified from accumulated other comprehensive income	30	(381)	(768)	(782)
Other comprehensive income (loss), net of tax	908	3,294	(17,481)	7,372
Accumulated other comprehensive income (loss), net of tax, end of period	(15,923)	4,879	(15,923)	4,879
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Net gain on securities transactions	0	666	1,434	1,398
Salaries and employee benefits	7,935	7,587	23,760	22,849
Income taxes	6,077	6,079	17,373	16,656
Net income	10,252	9,753	29,183	27,728
Reclassification Out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Net income	(30)	381	768	782
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	(14,696)	3,022	3,755	(1,018)
Other comprehensive income (loss)- before reclassifications	878	3,675	(16,713)	8,154
Amount reclassified from accumulated other comprehensive income	0	(400)	(860)	(839)
Other comprehensive income (loss), net of tax	878	3,275	(17,573)	7,315
Accumulated other comprehensive income (loss), net of tax, end of period	(13,818)	6,297	(13,818)	6,297
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	0	666	1,434	1,398
Income taxes	0	(266)	(574)	(559)
Net income	0	400	860	839
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	(2,135)	(1,437)	(2,197)	(1,475)
Other comprehensive income (loss)- before reclassifications	0	0	0	0
Amount reclassified from accumulated other comprehensive income	30	19	92	57
Other comprehensive income (loss), net of tax	30	19	92	57
Accumulated other comprehensive income (loss), net of tax, end of period	(2,105)	(1,418)	(2,105)	(1,418)
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	21	14	61	39
Net income	(30)	(19)	(92)	(57)
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	197	197
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	$ (117)	$ (99)	$ (350)	$ (293)