Summary of Investments (Maturities) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Held-To-Maturity, Amortized Cost
Due in one year or less	$ 55
Due after one year through five years	200
Due after five years through 10 years	0
Due after 10 years	0
Amortized Cost	356	$ 397
Held-To-Maturity, Fair Value
Due in one year or less	55
Due after one year through five years	200
Due after five years through 10 years	0
Due after 10 years	0
Fair Value	359	404
Available-For-Sale, Amortized Cost
Due in one year or less	178,468
Due after one year through five years	793,496
Due after five years through 10 years	930,136
Due after 10 years	479,748
Amortized Cost	2,843,014	2,845,217
Available-For-Sale, Fair Value
Due in one year or less	180,117
Due after one year through five years	826,094
Due after five years through 10 years	937,879
Due after 10 years	477,786
Fair Value	3,055,908	3,088,922
Trading, Amortized Cost
Due in one year or less	2,765
Due after one year through five years	6,629
Due after five years through 10 years	2,081
Due after 10 years	2,875
Amortized Cost	14,350	14,363
Trading, Fair Value
Due in one year or less	3,667
Due after one year through five years	6,733
Due after five years through 10 years	2,611
Due after 10 years	3,377
Fair Value	16,388	16,862
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	5,731
Amortized Cost	5,731	2,741
Available-For-Sale, Fair Value
Securities not categorized by contractual maturity	5,956
Fair Value	5,956	3,018
Mortgage-Backed Securities [Member]
Held-To-Maturity, Amortized Cost
Securities not categorized by contractual maturity	101
Amortized Cost	101	142
Held-To-Maturity, Fair Value
Securities not categorized by contractual maturity	104
Fair Value	104	149
Available-For-Sale, Amortized Cost
Securities not categorized by contractual maturity	15,096
Amortized Cost	15,096	17,121
Available-For-Sale, Fair Value
Securities not categorized by contractual maturity	15,521
Fair Value	15,521	17,558
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	368,182
Amortized Cost	368,182	335,092
Available-For-Sale, Fair Value
Securities not categorized by contractual maturity	368,008
Fair Value	368,008	337,289
Fixed Maturities [Member]
Held-To-Maturity, Amortized Cost
Amortized Cost	356	397
Held-To-Maturity, Fair Value
Fair Value	359	404
Available-For-Sale, Amortized Cost
Amortized Cost	2,770,857	2,773,566
Available-For-Sale, Fair Value
Fair Value	2,811,361	$ 2,843,079
Trading, Amortized Cost
Amortized Cost	14,350
Trading, Fair Value
Fair Value	$ 16,388