Accumulated Other Comprehensive Income Components of 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 [Roll Forward]
Beginning Balance	$ (32,466)	$ 482	$ 5,675	$ 7,955
Other comprehensive income (loss) before reclassifications	(7,057)	11,105	(42,452)	4,948
Amounts reclassified from accumulated other comprehensive loss	(1,348)	220	(4,094)	(1,096)
Ending Balance	(40,871)	11,807	(40,871)	11,807
Unrealized Gains on Investment Securities Not Other-Than-Temporarily Impaired [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(12,941)	19,122	26,361	27,054
Other comprehensive income (loss) before reclassifications	(6,951)	10,834	(43,784)	4,714
Amounts reclassified from accumulated other comprehensive loss	(1,774)	(40)	(4,243)	(1,852)
Ending Balance	(21,666)	29,916	(21,666)	29,916
Unrealized Non-Credit Losses on Other-Than-Temporarily Impaired Debt Securities [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	1,050	(1,048)	613	(1,011)
Other comprehensive income (loss) before reclassifications	(106)	271	1,332	234
Amounts reclassified from accumulated other comprehensive loss	63	12	(938)	12
Ending Balance	1,007	(765)	1,007	(765)
Unrealized Effective Portions of Losses on Forward-Starting Interest Rate Swaps [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(2,750)	(2,886)	(2,818)	(2,954)
Amounts reclassified from accumulated other comprehensive loss	34	34	102	102
Ending Balance	(2,716)	(2,852)	(2,716)	(2,852)
Unrecognized Pension and Postretirement Plan Items [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(17,825)	(14,706)	(18,481)	(15,134)
Amounts reclassified from accumulated other comprehensive loss	329	214	985	642
Ending Balance	$ (17,496)	$ (14,492)	$ (17,496)	$ (14,492)