Investments (Fair Value and Losses by Investment Category and Length of Time in a Loss Position) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	$ 64,520	$ 186,210
Less than 12 months Gross Unrealized Losses	991	4,855
Twelve months or more Fair Value	67,788	29,560
Twelve months or more Gross Unrealized Losses	1,603	4,348
Total Fair Value	132,308	215,770
Total Gross Unrealized Losses	2,594	9,203
US Treasury And Government [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	7,183
Less than 12 months Gross Unrealized Losses	271
Twelve months or more Fair Value	0
Twelve months or more Gross Unrealized Losses	0
Total Fair Value	7,183
Total Gross Unrealized Losses	271
Corporate Debt Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	37,216	129,881
Less than 12 months Gross Unrealized Losses	639	4,010
Twelve months or more Fair Value	35,863	1,130
Twelve months or more Gross Unrealized Losses	381	326
Total Fair Value	73,079	131,011
Total Gross Unrealized Losses	1,020	4,336
Asset-backed Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	15,455	48,831
Less than 12 months Gross Unrealized Losses	38	782
Twelve months or more Fair Value	31,925	28,430
Twelve months or more Gross Unrealized Losses	1,222	4,022
Total Fair Value	47,380	77,261
Total Gross Unrealized Losses	1,260	4,804
Commercial Mortgage Backed Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	4,666	7,014
Less than 12 months Gross Unrealized Losses	43	8
Twelve months or more Fair Value	0	0
Twelve months or more Gross Unrealized Losses	0	0
Total Fair Value	4,666	7,014
Total Gross Unrealized Losses	43	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	0	0
Twelve months or more Gross Unrealized Losses	0	0
Total Fair Value	0	484
Total Gross Unrealized Losses	$ 0	$ 55