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		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 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	$ (1,714)	$ 374	(1,145)	1,575
Other comprehensive income (loss)	453,682	(610,322)	757,210	(442,133)
Stockholders' equity, ending balance	4,877,758	4,306,056	4,877,758	4,306,056
Available for Sale Assets [Member]
Accumulated Other Comprehensive Income, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	634,337	1,261,518	332,333	1,090,273
Other comprehensive income (loss) before reclassifications, net of tax	453,586	(609,544)	756,680	(437,135)
Reclassifications, net of tax	(3,372)	(2,001)	(4,462)	(3,165)
Other comprehensive income (loss)	450,214	(611,545)	752,218	(440,300)
Stockholders' equity, ending balance	1,084,551	649,973	1,084,551	649,973
Deferred Acquisition Costs [Member]
Accumulated Other Comprehensive Income, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	(6,915)	(10,334)	(5,115)	(10,758)
Other comprehensive income (loss) before reclassifications, net of tax	(1,743)	1,919	(3,543)	2,343
Reclassifications, net of tax	0	0	0	0
Other comprehensive income (loss)	(1,743)	1,919	(3,543)	2,343
Stockholders' equity, ending balance	(8,658)	(8,415)	(8,658)	(8,415)
Foreign Exchange [Member]
Accumulated Other Comprehensive Income, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	4,847	11,424	3,627	17,386
Other comprehensive income (loss) before reclassifications, net of tax	3,484	(3,071)	4,704	(9,033)
Reclassifications, net of tax	0	0	0	0
Other comprehensive income (loss)	3,484	(3,071)	4,704	(9,033)
Stockholders' equity, ending balance	8,331	8,353	8,331	8,353
Pension Adjustments [Member]
Accumulated Other Comprehensive Income, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	(96,794)	(96,967)	(98,898)	(99,449)
Other comprehensive income (loss) before reclassifications, net of tax	69	0	514	117
Reclassifications, net of tax	1,658	2,375	3,317	4,740
Other comprehensive income (loss)	1,727	2,375	3,831	4,857
Stockholders' equity, ending balance	(95,067)	(94,592)	(95,067)	(94,592)
Total [Member]
Accumulated Other Comprehensive Income, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	535,475	1,165,641	231,947	997,452
Other comprehensive income (loss) before reclassifications, net of tax	455,396	(610,696)	758,355	(443,708)
Reclassifications, net of tax	(1,714)	374	(1,145)	1,575
Other comprehensive income (loss)	453,682	(610,322)	757,210	(442,133)
Stockholders' equity, ending balance	$ 989,157	$ 555,319	$ 989,157	$ 555,319