Other Comprehensive Income - Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Change in net unrealized Gain during period:
Change in net unrealized gain during period, before tax amount	$ (4,648)	$ 17,168	$ (8,438)
Change in net unrealized gain during period, tax expense (benefit)	(1,829)	6,899	(2,989)
Change in net unrealized gain during period, net of tax amount	(2,819)	10,269	(5,449)
Investment securities available-for-sale:
Reclassification adjustment for net gains included in net income, before tax amount	(348)	(1,544)	(170)
Reclassification adjustment for net, gains included in net income, tax expense (benefit)	(137)	(620)	(60)
Reclassification adjustment for net gains included in net income, net of tax amount	(211)	(924)	(110)
Unamortized Premium on Available-For-Sale Securities Transferred to Held-To-Maturity
Unamortized premium on available-to-sale securities transferred into held-for-maturity, before tax amount	56	389	722
Unamortized premium on available-to-sale securities transferred into held-for-maturity, tax expense (benefit)	22	156	256
Unamortized premium on available-to-sale securities transferred into held-for-maturity, net of tax amount	34	233	466
Change in net actuarial loss:
Change in net actuarial loss, before tax amount	(77)	135	(940)
Change in net actuarial loss, tax expense (benefit)	(30)	54	(333)
Change in net actuarial loss, net of tax amount	(47)	81	(607)
Other comprehensive income (Loss)
Other comprehensive income (loss), before tax	(5,017)	16,148	(8,826)
Total other comprehensive income, tax expense (benefit)	(1,974)	6,489	(3,126)
Other comprehensive income, net of tax	$ (3,043)	$ 9,659	$ (5,700)