Fair Value of Assets and Liabilities Fair Value of Assets and Liabilities (Quantitative Information for Level 3 Inputs) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Percentage Of Fixed Maturity Securities Classified As Level 3	5.90%	6.90%
Corporate Debt Securities [Member] | Market Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	$ 150,170	$ 167,815
Corporate Debt Securities [Member] | Weighted Average [Member] | Market Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount for Lack of Marketability	1.00%	1.00%
Corporate Debt Securities [Member] | Maximum [Member] | Market Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount for Lack of Marketability	2.00%	2.00%
Corporate Debt Securities [Member] | Minimum [Member] | Market Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount for Lack of Marketability	0.00%	0.00%
Longevity Swap [Member] | Income Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	$ 37,827	$ 26,958
Longevity Swap [Member] | Weighted Average [Member] | Income Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Long-Duration Contracts, Assumptions by Product and Guarantee, Mortality Rate, Low End	2.00%	2.00%
Fair Value Inputs Mortality Improvement	3.00%	3.00%
Longevity Swap [Member] | Maximum [Member] | Income Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Long-Duration Contracts, Assumptions by Product and Guarantee, Mortality Rate, Low End	100.00%	100.00%
Fair Value Inputs Mortality Improvement	10.00%	10.00%
Longevity Swap [Member] | Minimum [Member] | Income Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Long-Duration Contracts, Assumptions by Product and Guarantee, Mortality Rate, Low End	0.00%	0.00%
Fair Value Inputs Mortality Improvement	(10.00%)	(10.00%)
US Government Agencies Debt Securities [Member] | Weighted Average [Member] | Market Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount for Lack of Marketability	1.00%	1.00%
US Government Agencies Debt Securities [Member] | Maximum [Member] | Market Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount for Lack of Marketability	1.00%	1.00%
US Government Agencies Debt Securities [Member] | Minimum [Member] | Market Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount for Lack of Marketability	0.00%	0.00%
US States and Political Subdivisions Debt Securities [Member] | Market Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	$ 4,544	$ 4,670
US States and Political Subdivisions Debt Securities [Member] | Weighted Average [Member] | Market Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount for Lack of Marketability	1.00%	1.00%
US States and Political Subdivisions Debt Securities [Member] | Maximum [Member] | Market Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount for Lack of Marketability	1.00%	1.00%
US States and Political Subdivisions Debt Securities [Member] | Minimum [Member] | Market Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount for Lack of Marketability	1.00%	1.00%
Embedded Derivatives In Indexed Annuity [Member] | Income Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Financial and Nonfinancial Liabilities, Fair Value Disclosure	$ 821,821	$ 805,672
Embedded Derivatives In Indexed Annuity [Member] | Weighted Average [Member] | Income Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Long-Duration Contracts, Assumptions by Product and Guarantee, Lapse Rate, Low End	10.00%	8.00%
Long-Duration Contracts, Assumptions by Product and Guarantee, Mortality Rate, Low End	3.00%	2.00%
Fair Value Inputs Withdrawal	4.00%	3.00%
Fair Value Inputs Option Budget Projection	2.00%	2.00%
Embedded Derivatives In Indexed Annuity [Member] | Maximum [Member] | Income Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Long-Duration Contracts, Assumptions by Product and Guarantee, Lapse Rate, Low End	35.00%	35.00%
Long-Duration Contracts, Assumptions by Product and Guarantee, Mortality Rate, Low End	100.00%	100.00%
Fair Value Inputs Withdrawal	5.00%	5.00%
Fair Value Inputs Option Budget Projection	4.00%	4.00%
Embedded Derivatives In Indexed Annuity [Member] | Minimum [Member] | Income Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Long-Duration Contracts, Assumptions by Product and Guarantee, Lapse Rate, Low End	0.00%	0.00%
Long-Duration Contracts, Assumptions by Product and Guarantee, Mortality Rate, Low End	0.00%	0.00%
Fair Value Inputs Withdrawal	0.00%	0.00%
Fair Value Inputs Option Budget Projection	2.00%	2.00%
Embedded Derivatives In Variable Annuity [Member] | Income Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Financial and Nonfinancial Liabilities, Fair Value Disclosure	$ 168,119	$ 184,636
Embedded Derivatives In Variable Annuity [Member] | Weighted Average [Member] | Income Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Long-Duration Contracts, Assumptions by Product and Guarantee, Lapse Rate, Low End	5.00%	6.00%
Long-Duration Contracts, Assumptions by Product and Guarantee, Mortality Rate, Low End	1.00%	2.00%
Fair Value Inputs Withdrawal	3.00%	3.00%
Embedded Derivatives In Variable Annuity [Member] | Maximum [Member] | Income Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Long-Duration Contracts, Assumptions by Product and Guarantee, Lapse Rate, Low End	25.00%	25.00%
Long-Duration Contracts, Assumptions by Product and Guarantee, Mortality Rate, Low End	100.00%	100.00%
Fair Value Inputs Withdrawal	7.00%	7.00%
Embedded Derivatives In Variable Annuity [Member] | Minimum [Member] | Income Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Long-Duration Contracts, Assumptions by Product and Guarantee, Lapse Rate, Low End	0.00%	0.00%
Long-Duration Contracts, Assumptions by Product and Guarantee, Mortality Rate, Low End	0.00%	0.00%
Fair Value Inputs Withdrawal	0.00%	0.00%
Embedded Derivatives In Variable Annuity Contracts [Member] | Weighted Average [Member] | Income Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Entity Credit Risk	1.00%	1.00%
Fair Value Assumptions, Expected Volatility Rate	9.00%	14.00%
Embedded Derivatives In Variable Annuity Contracts [Member] | Maximum [Member] | Income Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Entity Credit Risk	5.00%	5.00%
Fair Value Assumptions, Expected Volatility Rate	27.00%	27.00%
Embedded Derivatives In Variable Annuity Contracts [Member] | Minimum [Member] | Income Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Entity Credit Risk	0.00%	0.00%
Fair Value Assumptions, Expected Volatility Rate	0.00%	0.00%
Mortality Swap [Member] | Income Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Financial and Nonfinancial Liabilities, Fair Value Disclosure	$ 1,683	$ 2,462
Mortality Swap [Member] | Weighted Average [Member] | Income Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Long-Duration Contracts, Assumptions by Product and Guarantee, Mortality Rate, Low End	1.00%	1.00%
Mortality Swap [Member] | Maximum [Member] | Income Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Long-Duration Contracts, Assumptions by Product and Guarantee, Mortality Rate, Low End	100.00%	100.00%
Mortality Swap [Member] | Minimum [Member] | Income Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Long-Duration Contracts, Assumptions by Product and Guarantee, Mortality Rate, Low End	0.00%	0.00%
Total Return Swap [Member] | Funds Withheld At Interest Embedded Derivatives [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	$ 84,325	$ (22,529)
Total Return Swap [Member] | Funds Withheld At Interest Embedded Derivatives [Member] | Weighted Average [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Long-Duration Contracts, Assumptions by Product and Guarantee, Lapse Rate, Low End	10.00%	8.00%
Long-Duration Contracts, Assumptions by Product and Guarantee, Mortality Rate, Low End	3.00%	2.00%
Fair Value Inputs Withdrawal	4.00%	3.00%
Fair Value Inputs, Entity Credit Risk	1.00%	1.00%
Fair Value Inputs Credit Rate	3.00%	2.00%
Total Return Swap [Member] | Funds Withheld At Interest Embedded Derivatives [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Long-Duration Contracts, Assumptions by Product and Guarantee, Lapse Rate, Low End	35.00%	35.00%
Long-Duration Contracts, Assumptions by Product and Guarantee, Mortality Rate, Low End	100.00%	100.00%
Fair Value Inputs Withdrawal	5.00%	5.00%
Fair Value Inputs, Entity Credit Risk	5.00%	5.00%
Fair Value Inputs Credit Rate	4.00%	4.00%
Total Return Swap [Member] | Funds Withheld At Interest Embedded Derivatives [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Long-Duration Contracts, Assumptions by Product and Guarantee, Lapse Rate, Low End	0.00%	0.00%
Long-Duration Contracts, Assumptions by Product and Guarantee, Mortality Rate, Low End	0.00%	0.00%
Fair Value Inputs Withdrawal	0.00%	0.00%
Fair Value Inputs, Entity Credit Risk	0.00%	0.00%
Fair Value Inputs Credit Rate	2.00%	2.00%
Total Return Swap [Member] | US Government Agencies Debt Securities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	$ 23,251	$ 24,488