Investments (Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Amortized cost and fair value of fixed maturity securities investments classified by contractual maturity date
Due in 1 year or less, Available for sale, Cost or amortized cost	$ 164,158
Due after 1 year through 5 years, Available for sale, Cost or amortized cost	1,133,253
Due after 5 years through 10 years, Available for sale, Cost or amortized cost	1,223,353
Due after 10 years through 15 years, Available for sale, Cost or amortized cost	874,072
Due after 15 years, Available for sale, Cost or amortized cost	1,058,726
Securities with contractual maturities, Available for sale, Cost or amortized cost	4,453,562
Mortgage-backed and asset-backed securities, Available for sale, Cost or amortized cost	1,678,684
Available-for-sale fixed maturity Securities, Amortized Cost Basis	6,132,246	$ 6,352,737
Due in 1 year or less, Available for sale, Fair value	160,738
Due after 1 year through 5 years, Available for sale, Fair value	1,158,235
Due after 5 years through 10 years, Available for sale, Fair value	1,277,278
Due after 10 years through 15 years, Available for sale, Fair value	914,971
Due after 15 years, Available for sale, Fair value	1,087,517
Securities with contractual maturities, Available for sale, Fair value	4,598,739
Mortgage-backed and asset-backed securities, Available for sale, Fair value	1,697,517
Available-for-sale Securities, Fixed Maturity Securities, Fair value	$ 6,296,256	$ 6,610,368