Supplemental Information about Changes to Accumulated Other Comprehensive Income - Schedule of Analysis of Change in Balance by Component of Accumulated 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
Accumulated Other Comprehensive Income, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance			$ 4,055,552	$ 4,697,466
Reclassifications, net of tax	$ (1,229)	$ (2,252)	(2,373)	(678)
Other comprehensive income (loss)	153,669	(55,490)	910,879	(497,623)
Stockholders' equity, ending balance	5,086,383	4,283,302	5,086,383	4,283,302
Available for Sale Assets [Member]
Accumulated Other Comprehensive Income, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	1,084,551	649,973	332,333	1,090,273
Other comprehensive income (loss) before reclassifications, net of tax	154,389	(48,306)	911,069	(485,441)
Reclassifications, net of tax	(2,886)	(4,621)	(7,348)	(7,786)
Other comprehensive income (loss)	151,503	(52,927)	903,721	(493,227)
Stockholders' equity, ending balance	1,236,054	597,046	1,236,054	597,046
Deferred Acquisition Costs [Member]
Accumulated Other Comprehensive Income, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	(8,658)	(8,415)	(5,115)	(10,758)
Other comprehensive income (loss) before reclassifications, net of tax	405	934	(3,138)	3,277
Reclassifications, net of tax	0	0	0	0
Other comprehensive income (loss)	405	934	(3,138)	3,277
Stockholders' equity, ending balance	(8,253)	(7,481)	(8,253)	(7,481)
Foreign Exchange [Member]
Accumulated Other Comprehensive Income, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	8,331	8,353	3,627	17,386
Other comprehensive income (loss) before reclassifications, net of tax	104	(5,867)	4,808	(14,900)
Reclassifications, net of tax	0	0	0	0
Other comprehensive income (loss)	104	(5,867)	4,808	(14,900)
Stockholders' equity, ending balance	8,435	2,486	8,435	2,486
Pension Adjustments [Member]
Accumulated Other Comprehensive Income, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	(95,067)	(94,592)	(98,898)	(99,449)
Other comprehensive income (loss) before reclassifications, net of tax	0	1	513	119
Reclassifications, net of tax	1,657	2,369	4,975	7,108
Other comprehensive income (loss)	1,657	2,370	5,488	7,227
Stockholders' equity, ending balance	(93,410)	(92,222)	(93,410)	(92,222)
Total [Member]
Accumulated Other Comprehensive Income, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	989,157	555,319	231,947	997,452
Other comprehensive income (loss) before reclassifications, net of tax	154,898	(53,238)	913,252	(496,945)
Reclassifications, net of tax	(1,229)	(2,252)	(2,373)	(678)
Other comprehensive income (loss)	153,669	(55,490)	910,879	(497,623)
Stockholders' equity, ending balance	$ 1,142,826	$ 499,829	$ 1,142,826	$ 499,829