Investments (Fair Value and Losses by Investment Category and Length of Time in a Loss Position) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	$ 59,481	$ 186,210
Less than 12 months Gross Unrealized Losses	1,299	4,855
Twelve months or more Fair Value	17,861	29,560
Twelve months or more Gross Unrealized Losses	620	4,348
Total Fair Value	77,342	215,770
Total Gross Unrealized Losses	1,919	9,203
US Treasury And Government [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	7,090
Less than 12 months Gross Unrealized Losses	350
Twelve months or more Fair Value	0
Twelve months or more Gross Unrealized Losses	0
Total Fair Value	7,090
Total Gross Unrealized Losses	350
Corporate Debt Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	35,248	129,881
Less than 12 months Gross Unrealized Losses	897	4,010
Twelve months or more Fair Value	14,867	1,130
Twelve months or more Gross Unrealized Losses	330	326
Total Fair Value	50,115	131,011
Total Gross Unrealized Losses	1,227	4,336
Asset-backed Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	13,817	48,831
Less than 12 months Gross Unrealized Losses	42	782
Twelve months or more Fair Value	2,994	28,430
Twelve months or more Gross Unrealized Losses	290	4,022
Total Fair Value	16,811	77,261
Total Gross Unrealized Losses	332	4,804
Commercial Mortgage Backed Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	3,326	7,014
Less than 12 months Gross Unrealized Losses	10	8
Twelve months or more Fair Value	0	0
Twelve months or more Gross Unrealized Losses	0	0
Total Fair Value	3,326	7,014
Total Gross Unrealized Losses	10	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