Investments (Fixed Maturities and Equity Securities Excluding Investments Classified as Trading) (Details) (USD $)	Jun. 30, 2012		Dec. 31, 2011
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Fixed maturities, available-for-sale, amortized cost	$ 4,386,806,000		$ 4,838,695,000
Available-for-sale equity securities amortized cost basis	2,516,000		2,510,000
Fair Value, Fixed maturities, available for sale	4,778,391,000		5,273,767,000
Equity securities, available for sale	3,205,000		3,071,000
Net unrealized gains on impaired securities relating to changes in value of securities subsequent to the impairment measurement date	4,200,000		2,400,000
US Treasury And Government [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Fixed maturities, available-for-sale, amortized cost	45,413,000		85,196,000
Fair Value, Fixed maturities, available for sale	45,739,000		86,035,000
Obligations of U.S. states and their political subdivisions [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Fixed maturities, available-for-sale, amortized cost	91,615,000		90,807,000
Fair Value, Fixed maturities, available for sale	101,000,000		100,075,000
Foreign Government Debt Securities [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Fixed maturities, available-for-sale, amortized cost	100,019,000		120,361,000
Fair Value, Fixed maturities, available for sale	113,831,000		134,810,000
All other corporate securities
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Fixed maturities, available-for-sale, amortized cost	3,200,295,000		3,526,879,000
Fair Value, Fixed maturities, available for sale	3,517,142,000		3,887,713,000
Asset-backed Securities [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Fixed maturities, available-for-sale, amortized cost	180,305,000	[1]	172,390,000	[1]
Fair Value, Fixed maturities, available for sale	187,990,000	[1]	177,384,000	[1]
Commercial Mortgage Backed Securities [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Fixed maturities, available-for-sale, amortized cost	418,297,000		463,576,000
Fair Value, Fixed maturities, available for sale	445,795,000		491,757,000
Residential Mortgage Backed Securities [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Fixed maturities, available-for-sale, amortized cost	350,862,000	[2]	379,486,000	[2]
Fair Value, Fixed maturities, available for sale	366,894,000	[2]	395,993,000	[2]
Fixed Maturities [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Gross Unrealized Gains	395,299,000		444,275,000
Gross Unrealized Losses	3,714,000		9,203,000
Other-than-temporary impairments in AOCI	3,682,000	[3]	4,197,000	[4]
Fixed Maturities [Member] | US Treasury And Government [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Gross Unrealized Gains	326,000		839,000
Gross Unrealized Losses	0		0
Other-than-temporary impairments in AOCI	0	[3]	0	[4]
Fixed Maturities [Member] | Obligations of U.S. states and their political subdivisions [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Gross Unrealized Gains	9,385,000		9,268,000
Gross Unrealized Losses	0		0
Other-than-temporary impairments in AOCI	0	[3]	0	[4]
Fixed Maturities [Member] | Foreign Government Debt Securities [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Gross Unrealized Gains	13,812,000		14,449,000
Gross Unrealized Losses	0		0
Other-than-temporary impairments in AOCI	0	[3]	0	[4]
Fixed Maturities [Member] | All other corporate securities
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Gross Unrealized Gains	319,151,000		365,170,000
Gross Unrealized Losses	2,304,000		4,336,000
Other-than-temporary impairments in AOCI	0	[3]	236,000	[4]
Fixed Maturities [Member] | Asset-backed Securities [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Gross Unrealized Gains	9,075,000	[1]	9,798,000	[1]
Gross Unrealized Losses	1,390,000	[1]	4,804,000	[1]
Other-than-temporary impairments in AOCI	3,631,000	[1],[3]	3,906,000	[1],[4]
Fixed Maturities [Member] | Commercial Mortgage Backed Securities [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Gross Unrealized Gains	27,509,000		28,189,000
Gross Unrealized Losses	11,000		8,000
Other-than-temporary impairments in AOCI	0	[3]	0	[4]
Fixed Maturities [Member] | Residential Mortgage Backed Securities [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Gross Unrealized Gains	16,041,000	[2]	16,562,000	[2]
Gross Unrealized Losses	9,000	[2]	55,000	[2]
Other-than-temporary impairments in AOCI	51,000	[2],[3]	55,000	[2],[4]
Equity Securities Available For Sale [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Gross Unrealized Gains	689,000		561,000
Gross Unrealized Losses	0		0
Other-than-temporary impairments in AOCI	$ 0	[3]	$ 0	[4]

[1] Includes credit tranched securities collateralized by sub-prime mortgages, credit cards, education loans, and other asset types.

[2] Includes publicly-traded agency pass-through securities and collateralized mortgage obligations.

[3] Represents the amount of other-than-temporary impairment losses in “AOCI,” which were not included in earnings. Amount excludes $4.2 million of net unrealized gains on impaired securities relating to changes in the value of such securities subsequent to the impairment measurement date.

[4] Represents the amount of other-than-temporary impairment losses in AOCI, which were not included in earnings. Amount excludes $2.4 million of net unrealized gains on impaired securities relating to changes in the value of such securities subsequent to the impairment measurement date.