Summary of Investments (Maturities) (Details) - USD ($) $ in Thousands	Jun. 30, 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	658	$ 672
Held-To-Maturity, Fair Value
Due in one year or less	0
Due after one year through five years	601
Due after five years through 10 years	0
Due after 10 years	0
Fair Value	660	675
Available-For-Sale, Amortized Cost
Due in one year or less	94,578
Due after one year through five years	839,695
Due after five years through 10 years	910,131
Due after 10 years	556,331
Amortized Cost	2,880,838	2,861,583
Available-For-Sale, Fair Value
Due in one year or less	95,444
Due after one year through five years	870,386
Due after five years through 10 years	958,551
Due after 10 years	587,166
Fair Value	3,191,544	3,061,208
Trading, Amortized Cost
Due in one year or less	1,186
Due after one year through five years	7,158
Due after five years through 10 years	850
Due after 10 years	1,846
Amortized Cost	11,040	11,475
Trading, Fair Value
Due in one year or less	1,341
Due after one year through five years	8,174
Due after five years through 10 years	1,065
Due after 10 years	1,978
Fair Value	12,558	12,622
Fixed Maturities [Member]
Held-To-Maturity, Amortized Cost
Amortized Cost	658	672
Held-To-Maturity, Fair Value
Fair Value	660	675
Available-For-Sale, Amortized Cost
Amortized Cost	2,812,091	2,793,069
Available-For-Sale, Fair Value
Fair Value	2,942,364	2,824,961
Trading, Amortized Cost
Amortized Cost	11,040
Trading, Fair Value
Fair Value	12,558
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	4,643
Amortized Cost	4,643	5,461
Available-For-Sale, Fair Value
Securities not categorized by contractual maturity	4,812
Fair Value	4,812	5,666
Mortgage-Backed Securities [Member]
Held-To-Maturity, Amortized Cost
Securities not categorized by contractual maturity	58
Amortized Cost	58	72
Held-To-Maturity, Fair Value
Securities not categorized by contractual maturity	59
Fair Value	59	74
Available-For-Sale, Amortized Cost
Securities not categorized by contractual maturity	19,609
Amortized Cost	19,609	16,413
Available-For-Sale, Fair Value
Securities not categorized by contractual maturity	20,072
Fair Value	20,072	$ 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	387,104
Available-For-Sale, Fair Value
Securities not categorized by contractual maturity	$ 405,933