Investments (Fair Value and Losses by Investment Category and Length of Time in a Loss Position) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	$ 159,780	$ 186,210
Less than 12 months Gross Unrealized Losses	1,311	4,855
Twelve months or more Fair Value	67,027	29,560
Twelve months or more Gross Unrealized Losses	2,403	4,348
Total Fair Value	226,807	215,770
Total Gross Unrealized Losses	3,714	9,203
Corporate Debt Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	151,947	129,881
Less than 12 months Gross Unrealized Losses	1,298	4,010
Twelve months or more Fair Value	35,717	1,130
Twelve months or more Gross Unrealized Losses	1,006	326
Total Fair Value	187,664	131,011
Total Gross Unrealized Losses	2,304	4,336
Asset-backed Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	3,760	48,831
Less than 12 months Gross Unrealized Losses	2	782
Twelve months or more Fair Value	30,831	28,430
Twelve months or more Gross Unrealized Losses	1,388	4,022
Total Fair Value	34,591	77,261
Total Gross Unrealized Losses	1,390	4,804
Commercial Mortgage Backed Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	4,073	7,014
Less than 12 months Gross Unrealized Losses	11	8
Twelve months or more Fair Value	0	0
Twelve months or more Gross Unrealized Losses	0	0
Total Fair Value	4,073	7,014
Total Gross Unrealized Losses	11	8
Residential Mortgage Backed Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	0	484
Less than 12 months Gross Unrealized Losses	0	55
Twelve months or more Fair Value	479	0
Twelve months or more Gross Unrealized Losses	9	0
Total Fair Value	479	484
Total Gross Unrealized Losses	$ 9	$ 55