Summary of Investments (Maturities) (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Held-To-Maturity, Amortized Cost
Due in one year or less	$ 0
Due after one year through five years	600
Due after five years through 10 years	0
Due after 10 years	0
Amortized Cost	664	$ 672
Held-To-Maturity, Fair Value
Due in one year or less	0
Due after one year through five years	602
Due after five years through 10 years	0
Due after 10 years	0
Fair Value	667	675
Available-For-Sale, Amortized Cost
Due in one year or less	88,221
Due after one year through five years	841,686
Due after five years through 10 years	934,933
Due after 10 years	519,020
Amortized Cost	2,839,442	2,861,583
Available-For-Sale, Fair Value
Due in one year or less	88,799
Due after one year through five years	865,457
Due after five years through 10 years	964,495
Due after 10 years	535,768
Fair Value	3,092,982	3,061,208
Trading, Amortized Cost
Due in one year or less	1,614
Due after one year through five years	7,701
Due after five years through 10 years	375
Due after 10 years	1,847
Amortized Cost	11,537	11,475
Trading, Fair Value
Due in one year or less	2,178
Due after one year through five years	8,401
Due after five years through 10 years	488
Due after 10 years	1,933
Fair Value	13,000	12,622
Fixed Maturities [Member]
Held-To-Maturity, Amortized Cost
Amortized Cost	664	672
Held-To-Maturity, Fair Value
Fair Value	667	675
Available-For-Sale, Amortized Cost
Amortized Cost	2,770,718	2,793,069
Available-For-Sale, Fair Value
Fair Value	2,855,166	2,824,961
Trading, Amortized Cost
Amortized Cost	11,537
Trading, Fair Value
Fair Value	13,000
Asset-Backed Securities [Member]
Held-To-Maturity, Amortized Cost
Securities not categorized by contractual maturity	0
Held-To-Maturity, Fair Value
Securities not categorized by contractual maturity	0
Available-For-Sale, Amortized Cost
Securities not categorized by contractual maturity	4,789
Amortized Cost	4,789	5,461
Available-For-Sale, Fair Value
Securities not categorized by contractual maturity	4,815
Fair Value	4,815	5,666
Mortgage-Backed Securities [Member]
Held-To-Maturity, Amortized Cost
Securities not categorized by contractual maturity	64
Amortized Cost	64	72
Held-To-Maturity, Fair Value
Securities not categorized by contractual maturity	65
Fair Value	65	74
Available-For-Sale, Amortized Cost
Securities not categorized by contractual maturity	15,352
Amortized Cost	15,352	16,413
Available-For-Sale, Fair Value
Securities not categorized by contractual maturity	15,799
Fair Value	15,799	$ 16,738
Collateralized Mortgage Obligations [Member]
Held-To-Maturity, Amortized Cost
Securities not categorized by contractual maturity	0
Held-To-Maturity, Fair Value
Securities not categorized by contractual maturity	0
Available-For-Sale, Amortized Cost
Securities not categorized by contractual maturity	366,717
Available-For-Sale, Fair Value
Securities not categorized by contractual maturity	$ 380,033