Fair Value of Assets and Liabilities (Balances of Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale:	$ 6,614,791	$ 6,194,564
Trading account assets:	65,815	49,661
Equity securities, available-for-sale	56,046	29,500
Separate account assets	106,289,140	109,194,192
Margin Deposit Assets	336,000	156,000
Embedded Derivative Net	5,661,000	4,994,000
Embedded Derivative Gross Asset	560,000	577,000
Embedded Derivative Gross Liability	6,221,000	5,571,000
Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale:	6,614,791	6,194,564
Trading account assets:	65,815	49,661
Equity securities, available-for-sale	56,046	29,500
Short-term investments	135,450	121,272
Cash equivalents	253,686	67,843
Other long-term investments	27,951	29,572
Reinsurance recoverables	5,388,800	4,897,545
Receivables from parent and affiliates	175,332	177,672
Sub-total excluding separate account assets	12,717,871	11,567,629
Separate account assets	106,289,140	109,194,192
Total assets	119,007,011	120,761,821
Future policy benefits	5,661,265	4,993,611
Payables to parent and affiliates	0	0
Total liabilities	5,661,265	4,993,611
Asset, Netting	(377,506)	(215,066)
Liability, Netting	(41,949)	(58,687)
Fair Value, Measurements, Recurring | Other long-term investments
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Asset, Netting	(377,506)	(215,066)
Fair Value, Measurements, Recurring | Payables to parent and affiliates
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Liability, Netting	(41,949)	(58,687)
U.S. Treasury securities and obligations of U.S. government authorities and agencies | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale:	96,015	92,082
Obligations of U.S. states and their political subdivisions | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale:	588,264	325,654
Foreign government bonds | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale:	66,845	38,498
All other corporate securities | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale:	4,881,261	4,697,158
Trading account assets:	45,574	42,131
Asset-backed securities | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale:	450,664	402,251
Trading account assets:	1,993	1,990
Commercial mortgage-backed securities | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale:	403,024	498,879
Residential mortgage-backed securities | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale:	128,718	140,042
Equity securities | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Trading account assets:	18,248	5,540
Level 1 | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale:	0	0
Trading account assets:	0	0
Equity securities, available-for-sale	49	107
Short-term investments	117,148	6,997
Cash equivalents	3,534	41,584
Other long-term investments	0	0
Reinsurance recoverables	0	0
Receivables from parent and affiliates	0	0
Sub-total excluding separate account assets	120,731	48,688
Separate account assets	0	0
Total assets	120,731	48,688
Future policy benefits	0	0
Payables to parent and affiliates	0	0
Total liabilities	0	0
Level 1 | U.S. Treasury securities and obligations of U.S. government authorities and agencies | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale:	0	0
Level 1 | Obligations of U.S. states and their political subdivisions | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale:	0	0
Level 1 | Foreign government bonds | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale:	0	0
Level 1 | All other corporate securities | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale:	0	0
Trading account assets:	0	0
Level 1 | Asset-backed securities | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale:	0	0
Trading account assets:	0	0
Level 1 | Commercial mortgage-backed securities | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale:	0	0
Level 1 | Residential mortgage-backed securities | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale:	0	0
Level 1 | Equity securities | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Trading account assets:	0	0
Level 2 | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale:	6,371,163	6,009,546
Trading account assets:	47,567	44,121
Equity securities, available-for-sale	55,823	28,643
Short-term investments	18,302	114,275
Cash equivalents	250,152	26,259
Other long-term investments	403,288	242,523
Reinsurance recoverables	0	0
Receivables from parent and affiliates	172,302	158,469
Sub-total excluding separate account assets	7,318,597	6,623,836
Separate account assets	105,927,551	108,891,268
Total assets	113,246,148	115,515,104
Future policy benefits	0	0
Payables to parent and affiliates	41,949	58,687
Total liabilities	41,949	58,687
Level 2 | U.S. Treasury securities and obligations of U.S. government authorities and agencies | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale:	96,015	92,082
Level 2 | Obligations of U.S. states and their political subdivisions | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale:	588,264	325,654
Level 2 | Foreign government bonds | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale:	66,845	38,498
Level 2 | All other corporate securities | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale:	4,792,914	4,612,357
Trading account assets:	45,574	42,131
Level 2 | Asset-backed securities | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale:	295,383	302,034
Trading account assets:	1,993	1,990
Level 2 | Commercial mortgage-backed securities | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale:	403,024	498,879
Level 2 | Residential mortgage-backed securities | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale:	128,718	140,042
Level 2 | Equity securities | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Trading account assets:	0	0
Level 3 | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale:	243,628	185,018
Trading account assets:	18,248	5,540
Equity securities, available-for-sale	174	750
Short-term investments	0	0
Cash equivalents	0	0
Other long-term investments	2,169	2,115
Reinsurance recoverables	5,388,800	4,897,545
Receivables from parent and affiliates	3,030	19,203
Sub-total excluding separate account assets	5,656,049	5,110,171
Separate account assets	361,589	302,924
Total assets	6,017,638	5,413,095
Future policy benefits	5,661,265	4,993,611
Payables to parent and affiliates	0	0
Total liabilities	5,661,265	4,993,611
Level 3 | U.S. Treasury securities and obligations of U.S. government authorities and agencies | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale:	0	0
Level 3 | Obligations of U.S. states and their political subdivisions | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale:	0	0
Level 3 | Foreign government bonds | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale:	0	0
Level 3 | All other corporate securities | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale:	88,347	84,801
Trading account assets:	0	0
Level 3 | Asset-backed securities | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale:	155,281	100,217
Trading account assets:	0	0
Level 3 | Commercial mortgage-backed securities | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale:	0	0
Level 3 | Residential mortgage-backed securities | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale:	0	0
Level 3 | Equity securities | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Trading account assets:	$ 18,248	$ 5,540