Accumulated Other Comprehensive Income (Components of Accumulated Other Comprehensive Income, Net of Tax) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance			$ 4,523,967
Total other comprehensive income (loss)	$ 102,014	$ (200,578)	208,705	$ (207,348)
Ending balance	4,608,071		4,608,071
Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	225,240	548,997	118,549	555,767
Change in accumulated other comprehensive income (loss) before reclassifications	105,909	(196,276)	327,272	(203,398)
Amounts reclassified from accumulated other comprehensive income	(3,895)	(4,302)	(118,567)	(3,950)
Total other comprehensive income (loss)	102,014	(200,578)	208,705	(207,348)
Ending balance	327,254	348,419	327,254	348,419
Foreign currency translation adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(258,874)	(193,662)	(270,734)	(127,711)
Change in accumulated other comprehensive income (loss) before reclassifications	(14,524)	20,151	(2,664)	(45,800)
Amounts reclassified from accumulated other comprehensive income	0	0	0	0
Total other comprehensive income (loss)	(14,524)	20,151	(2,664)	(45,800)
Ending balance	(273,398)	(173,511)	(273,398)	(173,511)
Unrealized gains on securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	525,315	850,541	495,443	793,082
Change in accumulated other comprehensive income (loss) before reclassifications	120,275	(216,522)	246,281	(155,127)
Amounts reclassified from accumulated other comprehensive income	(4,335)	(6,542)	(100,469)	(10,478)
Total other comprehensive income (loss)	115,940	(223,064)	145,812	(165,605)
Ending balance	641,255	627,477	641,255	627,477
OTTI
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	21,183	25,700	22,434	26,594
Change in accumulated other comprehensive income (loss) before reclassifications	158	95	(1,374)	(2,470)
Amounts reclassified from accumulated other comprehensive income	34	(376)	315	1,295
Total other comprehensive income (loss)	192	(281)	(1,059)	(1,175)
Ending balance	21,375	25,419	21,375	25,419
Pension under- funding
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(62,384)	(133,582)	(128,594)	(136,198)
Change in accumulated other comprehensive income (loss) before reclassifications	0	0	85,029	(1)
Amounts reclassified from accumulated other comprehensive income	406	2,616	(18,413)	5,233
Total other comprehensive income (loss)	406	2,616	66,616	5,232
Ending balance	$ (61,978)	$ (130,966)	$ (61,978)	$ (130,966)