Equity (Balance of and Changes in Each Component of AOCI) (Details) - USD ($) $ in Thousands		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015	Dec. 31, 2014
Accumulated other comprehensive income		$ 2,212,326	$ 906,479	$ 708,284	$ 1,657,129
Other Comprehensive Income (Loss), before Reclassifications, before Tax		2,254,015	(1,018,849)
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax		(104,892)	38,792
Other Comprehensive Income (Loss), Tax		645,081	(229,407)
Accumulated Translation Adjustment [Member]
Accumulated other comprehensive income		(121,709)	(119,493)	(181,151)	81,847
Other Comprehensive Income (Loss), before Reclassifications, before Tax		68,271	(176,562)
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax		0	0
Other Comprehensive Income (Loss), Tax		(8,829)	(24,778)
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated other comprehensive income	[1]	2,381,473	1,071,990	935,697	1,624,773
Other Comprehensive Income (Loss), before Reclassifications, before Tax	[1]	2,191,823	(843,541)
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	[1]	(109,145)	34,790
Other Comprehensive Income (Loss), Tax	[1]	636,902	(255,968)
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated other comprehensive income		(47,438)	(46,018)	$ (46,262)	$ (49,491)
Other Comprehensive Income (Loss), before Reclassifications, before Tax		(6,079)	1,254
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax		4,253	4,002
Other Comprehensive Income (Loss), Tax		$ (650)	$ 1,783

[1] Includes cash flow hedges of $(40,597) and $(29,397) as of September 30, 2016 and December 31, 2015, respectively, and $(37,167) and $(31,591) as of September 30, 2015 and December 31, 2014, respectively. See Note 5 - “Derivative Instruments” for additional information on cash flow hedges.