Fair Value of Assets and Liabilities (Quantitative Info for Level 3 Inputs) (Details) - USD ($) $ in Thousands		6 Months Ended	12 Months Ended
		Jun. 30, 2018	Dec. 31, 2017
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fixed maturities, trading, at fair value	[1]	$ 270,750	$ 166,360
Future policy benefits		7,194,626	9,132,569
Fair Value, Measurements, Recurring
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fixed maturities, trading, at fair value		270,750	166,360
Future policy benefits		$ 6,222,612	8,151,902
Level 3 | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Policyholder Age		50 years
Level 3 | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Policyholder Age		90 years
Level 3 | Fair Value, Measurements, Recurring
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fixed maturities, trading, at fair value		$ 0	0
Future policy benefits		$ 6,222,612	$ 8,151,902
Level 3 | Internal | Minimum | Discounted cash flow | Future policy benefits
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Lapse rate		1.00%	1.00%
Spread over LIBOR		0.19%	0.12%
Utilization rate		54.00%	52.00%
Withdrawal rate (greater than maximum range)		78.00%	78.00%
Mortality rate		0.00%	0.00%
Equity volatility curve		15.00%	13.00%
Level 3 | Internal | Minimum | Discounted cash flow | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Discount rate		4.40%	5.06%
Level 3 | Internal | Minimum | Liquidation | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Liquidation value		6.00%
Level 3 | Internal | Maximum | Discounted cash flow | Future policy benefits
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Lapse rate		13.00%	12.00%
Spread over LIBOR		1.28%	1.10%
Utilization rate		97.00%	97.00%
Withdrawal rate (greater than maximum range)		100.00%	100.00%
Mortality rate		15.00%	14.00%
Equity volatility curve		22.00%	24.00%
Level 3 | Internal | Maximum | Discounted cash flow | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Discount rate		20.82%	22.23%
Level 3 | Internal | Maximum | Liquidation | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Liquidation value		6.00%
Level 3 | Internal | Weighted Average | Discounted cash flow | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Discount rate		8.47%	8.57%
Level 3 | Internal | Weighted Average | Liquidation | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Liquidation value		6.00%
Level 3 | Internal | Fair Value, Measurements, Recurring | Future policy benefits
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Future policy benefits		$ 6,222,612	$ 8,151,902
Level 3 | Internal | Fair Value, Measurements, Recurring | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fixed maturities, trading, at fair value		25,336	22,215
Level 3 | Internal | Fair Value, Measurements, Recurring | Reinsurance Recoverables
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Reinsurance recoverables		$ 185,258	$ 244,006

[1] (1)Prior period amounts have been reclassified to conform to current period presentation. See "Adoption of ASU 2016-01" in Note 2 for details.