Accumulated Other Comprehensive Income (Loss) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 48,603	$ 65,602	$ 27,626
Other Comprehensive Income (Loss) Before Reclassifications	(122,403)	(29,050)	54,215
Amounts reclassified from accumulated other comprehensive income (loss)	3,852	1,008	8,311
Income tax (expense) benefit	45,704	11,043	(24,550)
Net other comprehensive income (loss) during period	(72,847)	(16,999)	37,976
Ending Balance	(24,244)	48,603	65,602
Investment Securities Available For Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	86,109	99,761	55,609
Other Comprehensive Income (Loss) Before Reclassifications	(158,207)	(19,042)	71,606
Amounts reclassified from accumulated other comprehensive income (loss)	(564)	(4,261)	1,112
Income tax (expense) benefit	61,266	9,651	(28,566)
Net other comprehensive income (loss) during period	(97,505)	(13,652)	44,152
Ending Balance	(11,396)	86,109	99,761
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(37,506)	(33,173)	(24,504)
Other Comprehensive Income (Loss) Before Reclassifications	35,804	(10,014)	(16,834)
Amounts reclassified from accumulated other comprehensive income (loss)	4,416	3,315	2,491
Income tax (expense) benefit	(15,562)	2,366	5,674
Net other comprehensive income (loss) during period	24,658	(4,333)	(8,669)
Ending Balance	(12,848)	(37,506)	(33,173)
Cash Flow Hedging Derivatives [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	0	(986)	(3,479)
Other Comprehensive Income (Loss) Before Reclassifications	0	6	(557)
Amounts reclassified from accumulated other comprehensive income (loss)	0	1,954	4,708
Income tax (expense) benefit	0	(974)	(1,658)
Net other comprehensive income (loss) during period	0	986	2,493
Ending Balance	$ 0	$ 0	$ (986)