Investments (Continuous Gross Unrealized Losses for Fixed Maturity and Equity Securities Available-For-Sale) (Details) $ in Thousands	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Total number of securities in an unrealized loss position less than 12 months	165	203
Total number of securities in an unrealized loss position equal to or greater than 12 months	28	35
Fixed maturity securities
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	$ 731,369	$ 947,335
Less than 12 Months Gross Unrealized Loss	22,632	27,973
Equal to or Greater than 12 Months Estimated Fair Value	39,199	52,129
Equal to or Greater than 12 Months Gross Unrealized Loss	4,589	6,922
U.S. corporate
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	223,324	250,559
Less than 12 Months Gross Unrealized Loss	4,950	6,667
Equal to or Greater than 12 Months Estimated Fair Value	17,757	17,745
Equal to or Greater than 12 Months Gross Unrealized Loss	1,299	1,616
U.S. government and agency
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	201,323	342,150
Less than 12 Months Gross Unrealized Loss	9,859	13,519
Equal to or Greater than 12 Months Estimated Fair Value	0	0
Equal to or Greater than 12 Months Gross Unrealized Loss	0	0
RMBS
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	105,822	137,470
Less than 12 Months Gross Unrealized Loss	2,016	2,089
Equal to or Greater than 12 Months Estimated Fair Value	5,773	6,822
Equal to or Greater than 12 Months Gross Unrealized Loss	106	233
Foreign corporate
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	125,659	129,093
Less than 12 Months Gross Unrealized Loss	4,193	3,541
Equal to or Greater than 12 Months Estimated Fair Value	11,031	22,965
Equal to or Greater than 12 Months Gross Unrealized Loss	2,681	4,529
CMBS
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	38,901	42,661
Less than 12 Months Gross Unrealized Loss	948	1,068
Equal to or Greater than 12 Months Estimated Fair Value	3,727	3,729
Equal to or Greater than 12 Months Gross Unrealized Loss	420	419
State and political subdivision
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	15,466	20,709
Less than 12 Months Gross Unrealized Loss	507	764
Equal to or Greater than 12 Months Estimated Fair Value	0	0
Equal to or Greater than 12 Months Gross Unrealized Loss	0	0
ABS
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	16,575	17,504
Less than 12 Months Gross Unrealized Loss	111	177
Equal to or Greater than 12 Months Estimated Fair Value	0	0
Equal to or Greater than 12 Months Gross Unrealized Loss	0	0
Foreign government
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	4,299	7,189
Less than 12 Months Gross Unrealized Loss	48	148
Equal to or Greater than 12 Months Estimated Fair Value	911	868
Equal to or Greater than 12 Months Gross Unrealized Loss	$ 83	$ 125