Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Components of Other Comprehensive Income (Loss) [Abstract]
Net unrealized holding (losses) gains arising during the period	$ (22,206)	$ 27,271	$ 142,852	$ (17,126)
Income tax benefit (expense)	7,772	(9,531)	(50,121)	5,955
Valuation allowance	0	77,555	0	62,383
Net of taxes	(14,434)	95,295	92,731	51,212
Net changes in benefit plan assets and obligations	(370)	(546)	(1,110)	(1,638)
Income tax benefit	129	192	388	574
Valuation allowance	0	(7,001)	0	(7,383)
Net of taxes	(241)	(7,355)	(722)	(8,447)
Net changes in unrealized foreign currency translation adjustment	(16)	(3,724)	(1,496)	(6,228)
Income tax benefit	6	1,306	522	2,186
Valuation allowance	0	(529)	0	(529)
Net of taxes	(10)	(2,947)	(974)	(4,571)
Total other comprehensive (loss) income	(22,592)	23,001	140,246	(24,992)
Total income tax benefit (expense), net of valuation allowance	7,907	61,992	(49,211)	63,186
Other comprehensive (loss) income, net of tax	(14,685)	84,993	91,035	38,194
Amounts Reclassified From Accumulated Other Comprehensive Income [Abstract]
Reclassification adjustment	83,749	127,248	352,676	378,685
Total income tax expense, net of valuation allowance	(27,131)	695,604	(117,646)	690,897
Valuation allowance	0	739,298	0	822,465
Net income	56,618	822,852	235,030	1,069,582
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period			2,236,140
Balance, end of period	2,583,079	2,148,519	2,583,079	2,148,519
Accumulated other comprehensive income (loss)
Components of Other Comprehensive Income (Loss) [Abstract]
Other comprehensive (loss) income, net of tax			91,035	38,194
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period			(60,880)	(81,341)
Other comprehensive income (loss) before reclassifications			96,706
Less: Amounts reclassified from accumulated other comprehensive income (loss)			5,671
Balance, end of period	30,155	(43,147)	30,155	(43,147)
Net unrealized gains and losses on available-for-sale securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period			(17,148)
Other comprehensive income (loss) before reclassifications			96,726
Less: Amounts reclassified from accumulated other comprehensive income (loss)			3,995
Balance, end of period	75,583		75,583
Net benefit plan assets and obligations recognized in shareholders' equity
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period			(44,652)
Other comprehensive income (loss) before reclassifications			0
Less: Amounts reclassified from accumulated other comprehensive income (loss)			722
Balance, end of period	(45,374)		(45,374)
Net unrealized foreign currency translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period			920
Other comprehensive income (loss) before reclassifications			(20)
Less: Amounts reclassified from accumulated other comprehensive income (loss)			954
Balance, end of period	(54)		(54)
Reclassification from Accumulated Other Comprehensive Income
Amounts Reclassified From Accumulated Other Comprehensive Income [Abstract]
Reclassification adjustment	5,618	(574)	8,535	12,229
Total income tax expense, net of valuation allowance	(1,966)	(18)	(2,864)	(62)
Net income	3,652	(592)	5,671	12,167
Reclassification from Accumulated Other Comprehensive Income | Net unrealized gains and losses on available-for-sale securities
Amounts Reclassified From Accumulated Other Comprehensive Income [Abstract]
Reclassification adjustment	5,248	(1,120)	5,958	10,591
Total income tax expense, net of valuation allowance	(1,837)	395	(1,963)	(3,697)
Valuation allowance	0	(413)	0	3,635
Net income	3,411	(1,138)	3,995	10,529
Reclassification from Accumulated Other Comprehensive Income | Net benefit plan assets and obligations recognized in shareholders' equity
Amounts Reclassified From Accumulated Other Comprehensive Income [Abstract]
Reclassification adjustment	370	546	1,110	1,638
Total income tax expense, net of valuation allowance	(129)	(192)	(388)	(574)
Valuation allowance	0	192	0	574
Net income	241	546	722	1,638
Reclassification from Accumulated Other Comprehensive Income | Net unrealized foreign currency translation
Amounts Reclassified From Accumulated Other Comprehensive Income [Abstract]
Reclassification adjustment	0	0	1,467	0
Total income tax expense, net of valuation allowance	0	0	(513)	0
Net income	$ 0	$ 0	$ 954	$ 0