Accumulated Other Comprehensive Income (Loss) Reclassifications Out of AOCI (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 (Loss) [Line Items]
Beginning Balance	$ 42,991	$ 65,278	$ 48,603	$ 65,602
Other comprehensive income (loss) before reclassification	(111,829)	1,281	(121,760)	(623)
Amounts reclassified from accumulated other comprehensive income (loss)	1,056	864	1,846	2,255
Income tax (expense) benefit	42,767	(844)	46,296	(655)
Net other comprehensive income (loss) during period	(68,006)	1,301	(73,618)	977
Ending Balance	(25,015)	66,579	(25,015)	66,579
Securities Available For Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	79,828	98,569	86,109	99,761
Other comprehensive income (loss) before reclassification	(111,829)	1,305	(121,760)	(609)
Amounts reclassified from accumulated other comprehensive income (loss)	(34)	(563)	(334)	(603)
Income tax (expense) benefit	43,188	(290)	47,138	472
Net other comprehensive income (loss) during period	(68,675)	452	(74,956)	(740)
Ending Balance	11,153	99,021	11,153	99,021
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(36,837)	(32,746)	(37,506)	(33,173)
Other comprehensive income (loss) before reclassification	0	0	0	0
Amounts reclassified from accumulated other comprehensive income (loss)	1,090	700	2,180	1,400
Income tax (expense) benefit	(421)	(273)	(842)	(546)
Net other comprehensive income (loss) during period	669	427	1,338	854
Ending Balance	(36,168)	(32,319)	(36,168)	(32,319)
Derivatives [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	0	(545)	0	(986)
Other comprehensive income (loss) before reclassification	0	(24)	0	(14)
Amounts reclassified from accumulated other comprehensive income (loss)	0	727	0	1,458
Income tax (expense) benefit	0	(281)	0	(581)
Net other comprehensive income (loss) during period	0	422	0	863
Ending Balance	$ 0	$ (123)	$ 0	$ (123)