Accumulated Other Comprehensive Income (Loss) (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) [Roll Forward]
Accumulated other comprehensive income (loss), Start of period	$ (33,868)		$ (44,778)		$ (18,245)		$ (45,615)
Reclassifications from accumulated other comprehensive income (loss) to net income
Reclassification adjustment of noncredit portion of impairment losses included in net income relating to HTM securities							351
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, before Tax	(11)		(17)		(31)		(52)
Other amounts of other comprehensive income (loss)
Net unrealized losses on available-for-sale securities	(5,822)		10,897		(25,314)		6,371
Non-credit portion of other-than-temporary impairment losses on held-to-maturity securities	0		0		0		(195)
Accretion of non-credit portion of other-than-temporary impairment losses to the carrying value of held-to-maturity securities	2,044		2,367		6,144		7,609
Prior service cost	0		0		(211)		0
Total other comprehensive income (loss)	(3,789)		13,247		(19,412)		14,084
Total Accumulated Other Comprehensive Income (Loss), End of period	(37,657)		(31,531)		(37,657)		(31,531)
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated other comprehensive income (loss), Start of period	3,035		671		22,527		5,197
Other amounts of other comprehensive income (loss)
Net unrealized losses on available-for-sale securities	(5,822)		10,897		(25,314)	[1]	6,371	[1]
Total other comprehensive income (loss)	(5,822)	[1]	10,897	[1]	(25,314)	[1]	6,371	[1]
Total Accumulated Other Comprehensive Income (Loss), End of period	(2,787)	[1]	11,568	[1]	(2,787)	[1]	11,568	[1]
Accumulated Other-than-Temporary Impairment [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated other comprehensive income (loss), Start of period	(37,337)		(46,031)		(41,437)		(51,429)
Reclassifications from accumulated other comprehensive income (loss) to net income
Reclassification adjustment of noncredit portion of impairment losses included in net income relating to HTM securities							351
Other amounts of other comprehensive income (loss)
Non-credit portion of other-than-temporary impairment losses on held-to-maturity securities							(195)
Accretion of non-credit portion of other-than-temporary impairment losses to the carrying value of held-to-maturity securities	2,044		2,367		6,144		7,609
Total other comprehensive income (loss)	2,044		2,367		6,144		7,765
Total Accumulated Other Comprehensive Income (Loss), End of period	(35,293)		(43,664)		(35,293)		(43,664)
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated other comprehensive income (loss), Start of period	434		582		665		617
Reclassifications from accumulated other comprehensive income (loss) to net income
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, before Tax	(11)		(17)		(31)		(52)
Other amounts of other comprehensive income (loss)
Prior service cost					(211)
Total other comprehensive income (loss)	(11)		(17)		(242)		(52)
Total Accumulated Other Comprehensive Income (Loss), End of period	$ 423		$ 565		$ 423		$ 565

[1] Net unrealized gains (losses) on available-for-sale securities are net of unrealized gains and losses relating to hedged interest rate risk included in net income.