Investments (Schedule of Amortized Cost and Fair Value of Fixed Maturity and Equity Securities) (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Investment Holdings [Line Items]
Held for investment, amortized cost	$ 76,773	$ 76,622
Held for investment	75,547	65,377
Fixed Maturity Securities [Member] \| Available For Sale Securities [Member]
Investment Holdings [Line Items]
Available for sale, amortized cost	39,199,077	35,823,710
Available for sale, gross unrealized gains	3,288,979	1,443,474
Available for sale, gross unrealized losses	(183,646)	(845,345)
Available for sale, fair value	42,304,410	36,421,839
Equity Securities [Member] \| Available For Sale Securities [Member]
Investment Holdings [Line Items]
Available for sale, amortized cost	7,520	7,515
Available for sale, gross unrealized gains	323	313
Available for sale, gross unrealized losses	0	0
Available for sale, fair value	7,843	7,828
United States Government Full Faith and Credit [Member] \| Fixed Maturity Securities [Member] \| Available For Sale Securities [Member]
Investment Holdings [Line Items]
Available for sale, amortized cost	416,503	470,567
Available for sale, gross unrealized gains	1,962	988
Available for sale, gross unrealized losses	0	(299)
Available for sale, fair value	418,465	471,256
United States Government Sponsored Agencies [Member] \| Fixed Maturity Securities [Member] \| Available For Sale Securities [Member]
Investment Holdings [Line Items]
Available for sale, amortized cost	1,410,760	1,386,219
Available for sale, gross unrealized gains	62,563	26,801
Available for sale, gross unrealized losses	(419)	(14,409)
Available for sale, fair value	1,472,904	1,398,611
United States Municipalities, States and Territories [Member] \| Fixed Maturity Securities [Member] \| Available For Sale Securities [Member]
Investment Holdings [Line Items]
Available for sale, amortized cost	3,548,586	3,422,667
Available for sale, gross unrealized gains	503,992	341,328
Available for sale, gross unrealized losses	(368)	(8,628)
Available for sale, fair value	4,052,210	3,755,367
Foreign Government Obligations [Member] \| Fixed Maturity Securities [Member] \| Available For Sale Securities [Member]
Investment Holdings [Line Items]
Available for sale, amortized cost	233,825	210,953
Available for sale, gross unrealized gains	24,420	12,547
Available for sale, gross unrealized losses	(3,825)	(10,935)
Available for sale, fair value	254,420	212,565
Corporate Securities [Member] \| Fixed Maturity Securities [Member] \| Available For Sale Securities [Member]
Investment Holdings [Line Items]
Available for sale, amortized cost	25,751,501	23,597,530
Available for sale, gross unrealized gains	2,298,306	887,288
Available for sale, gross unrealized losses	(134,150)	(682,424)
Available for sale, fair value	27,915,657	23,802,394
Corporate Securities [Member] \| Fixed Maturity Securities [Member] \| Held For Investment Securities [Member]
Investment Holdings [Line Items]
Held for investment, amortized cost	76,773	76,622
Held for investment, gross unrealized gains	0	0
Held for investment, gross unrealized losses	(1,226)	(11,245)
Held for investment	75,547	65,377
Residential Mortgage Backed Securities [Member] \| Fixed Maturity Securities [Member] \| Available For Sale Securities [Member]
Investment Holdings [Line Items]
Available for sale, amortized cost	1,225,720	1,366,985
Available for sale, gross unrealized gains	134,685	98,576
Available for sale, gross unrealized losses	(2,231)	(3,489)
Available for sale, fair value	1,358,174	1,462,072
Commercial Mortgage Backed Securities [Member] \| Fixed Maturity Securities [Member] \| Available For Sale Securities [Member]
Investment Holdings [Line Items]
Available for sale, amortized cost	5,121,361	4,238,265
Available for sale, gross unrealized gains	216,346	41,412
Available for sale, gross unrealized losses	(27,551)	(105,281)
Available for sale, fair value	5,310,156	4,174,396
Other Asset Backed Securities [Member] \| Fixed Maturity Securities [Member] \| Available For Sale Securities [Member]
Investment Holdings [Line Items]
Available for sale, amortized cost	1,490,821	1,130,524
Available for sale, gross unrealized gains	46,705	34,534
Available for sale, gross unrealized losses	(15,102)	(19,880)
Available for sale, fair value	$ 1,522,424	$ 1,145,178

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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