Investments (Amortized Cost and Fair Value of Fixed Maturities by Contractual Maturities) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Amortized Cost
Due in one year or less	$ 247,417
Due after one year through five years	770,481
Due after five years through ten years	470,280
Due after ten years	391,804
Amortized Cost	2,391,318	$ 2,609,253
Fair Value
Due in one year or less	249,765
Due after one year through five years	817,715
Due after five years through ten years	506,630
Due after ten years	431,123
Fixed maturities, available-for-sale, at fair value (amortized cost, 2015: $2,391,318; 2014: $2,609,253)	2,533,299	$ 2,800,593
Commercial mortgage-backed securities
Amortized Cost
Debt Maturities, without single maturity date	253,314
Fair Value
Debt Maturities, without Single Maturity Date	259,898
Residential mortgage-backed securities
Amortized Cost
Debt Maturities, without single maturity date	111,464
Fair Value
Debt Maturities, without Single Maturity Date	117,137
Asset-backed securities
Amortized Cost
Debt Maturities, without single maturity date	146,558
Fair Value
Debt Maturities, without Single Maturity Date	$ 151,031