Accumulated Other Comprehensive Income Components of 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 [Roll Forward]
Beginning Balance	$ 5,637	$ 12,109	$ 5,675	$ 7,955
Other comprehensive income (loss) before reclassifications	(36,603)	(10,876)	(35,395)	(6,120)
Amounts reclassified from accumulated other comprehensive loss	(1,500)	(751)	(2,746)	(1,353)
Ending Balance	(32,466)	482	(32,466)	482
Unrealized Gains on Investment Securities Not Other-Than-Temporarily Impaired [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	24,878	30,825	26,361	27,054
Other comprehensive income (loss) before reclassifications	(36,958)	(10,704)	(36,833)	(6,120)
Amounts reclassified from accumulated other comprehensive loss	(861)	(999)	(2,469)	(1,812)
Ending Balance	(12,941)	19,122	(12,941)	19,122
Unrealized Non-Credit Losses on Other-Than-Temporarily Impaired Debt Securities [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	1,696	(876)	613	(1,011)
Other comprehensive income (loss) before reclassifications	355	(172)	1,438	0
Amounts reclassified from accumulated other comprehensive loss	(1,001)	0	(1,001)	(37)
Ending Balance	1,050	(1,048)	1,050	(1,048)
Unrealized Effective Portions of Losses on Forward-Starting Interest Rate Swaps [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(2,784)	(2,920)	(2,818)	(2,954)
Amounts reclassified from accumulated other comprehensive loss	34	34	68	68
Ending Balance	(2,750)	(2,886)	(2,750)	(2,886)
Unrecognized Pension and Postretirement Plan Items [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(18,153)	(14,920)	(18,481)	(15,134)
Amounts reclassified from accumulated other comprehensive loss	328	214	656	428
Ending Balance	$ (17,825)	$ (14,706)	$ (17,825)	$ (14,706)