Accumulated Other Comprehensive Income (Loss) Reclassifications Out of AOCI (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 10,494	$ (25,015)	$ (24,244)	$ 48,603
Other comprehensive income (loss) before reclassification	(20,123)	(20,558)	36,061	(142,318)
Amounts reclassified from accumulated other comprehensive income (loss)	275	842	525	2,688
Income tax (expense) benefit	7,629	7,611	(14,067)	53,907
Total other comprehensive income (loss)	(12,219)	(12,105)	22,519	(85,723)
Ending Balance	(1,725)	(37,120)	(1,725)	(37,120)
Securities Available For Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	22,935	11,153	(11,396)	86,109
Other comprehensive income (loss) before reclassification	(20,123)	(20,558)	36,061	(142,318)
Amounts reclassified from accumulated other comprehensive income (loss)	(57)	(248)	(469)	(582)
Income tax (expense) benefit	7,757	8,031	(13,684)	55,169
Total other comprehensive income (loss)	(12,423)	(12,775)	21,908	(87,731)
Ending Balance	10,512	(1,622)	10,512	(1,622)
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(12,441)	(36,168)	(12,848)	(37,506)
Other comprehensive income (loss) before reclassification	0	0	0	0
Amounts reclassified from accumulated other comprehensive income (loss)	332	1,090	994	3,270
Income tax (expense) benefit	(128)	(420)	(383)	(1,262)
Total other comprehensive income (loss)	204	670	611	2,008
Ending Balance	$ (12,237)	$ (35,498)	$ (12,237)	$ (35,498)