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, 2013	Dec. 31, 2012
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	$ 526,055	$ 59,481
Less than 12 months Gross Unrealized Losses	22,025	1,299
Twelve months or more Fair Value	11,913	17,861
Twelve months or more Gross Unrealized Losses	1,988	620
Total Fair Value	537,968	77,342
Total Gross Unrealized Losses	24,013	1,919
Obligations of U.S. states and their political subdivisions [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	5,550	7,090
Less than 12 months Gross Unrealized Losses	464	350
Twelve months or more Fair Value	6,285	0
Twelve months or more Gross Unrealized Losses	1,113	0
Total Fair Value	11,835	7,090
Total Gross Unrealized Losses	1,577	350
Corporate Debt Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	423,896	35,248
Less than 12 months Gross Unrealized Losses	16,593	897
Twelve months or more Fair Value	5,510	14,867
Twelve months or more Gross Unrealized Losses	875	330
Total Fair Value	429,406	50,115
Total Gross Unrealized Losses	17,468	1,227
Asset-backed Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	26,645	13,817
Less than 12 months Gross Unrealized Losses	144	42
Twelve months or more Fair Value	0	2,994
Twelve months or more Gross Unrealized Losses	0	290
Total Fair Value	26,645	16,811
Total Gross Unrealized Losses	144	332
Commercial Mortgage Backed Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	63,450	3,326
Less than 12 months Gross Unrealized Losses	4,646	10
Twelve months or more Fair Value	118	0
Twelve months or more Gross Unrealized Losses	0	0
Total Fair Value	63,568	3,326
Total Gross Unrealized Losses	4,646	10
Residential Mortgage Backed Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	6,514	0
Less than 12 months Gross Unrealized Losses	178	0
Twelve months or more Fair Value	0	0
Twelve months or more Gross Unrealized Losses	0	0
Total Fair Value	6,514	0
Total Gross Unrealized Losses	$ 178	$ 0