Investments (Amortized Cost and Fair Value of Fixed Maturities by Contractual Maturities) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Available for Sale Amortized Cost
Due in one year or less	$ 250,546
Due after one year through five years	951,580
Due after five years through ten years	549,906
Due after ten years	411,017
Total	2,784,393	3,079,002
Available for Sale Securities Fair Value
Due in one year or less	257,895
Due after one year through five years	1,025,776
Due after five years through ten years	608,317
Due after ten years	476,453
Total	3,015,527	3,264,216
Residential Mortgage Backed Securities [Member]
Available for Sale Amortized Cost
Debt Maturities, without single maturity date	139,465
Available for Sale Securities Fair Value
Debt Maturities, without Single Maturity Date	146,840
Commercial Mortgage Backed Securities [Member]
Available for Sale Amortized Cost
Debt Maturities, without single maturity date	316,199
Available for Sale Securities Fair Value
Debt Maturities, without Single Maturity Date	327,743
Asset-backed Securities [Member]
Available for Sale Amortized Cost
Debt Maturities, without single maturity date	165,680
Available for Sale Securities Fair Value
Debt Maturities, without Single Maturity Date	$ 172,503