Fair Value of Assets and Liabilities (Quantitative Info for Level 3 Inputs) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Future policy benefits	$ 8,971,369	$ 8,686,196
Fair Value, Measurements, Recurring
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Future policy benefits	$ 7,999,051	7,707,333
Level 3 | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Policyholder Age	35 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]
Future policy benefits	$ 7,999,051	$ 7,707,333
Level 3 | Internal | Minimum | Discounted cash flow | Future policy benefits
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Lapse rate	1.00%	0.00%
Spread over LIBOR	0.13%	0.25%
Utilization rate	52.00%	52.00%
Withdrawal rate (greater than maximum range)	78.00%	78.00%
Mortality rate	0.00%	0.00%
Equity volatility curve	13.00%	16.00%
Level 3 | Internal | Minimum | Discounted cash flow | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Discount rate	1.38%	3.24%
Level 3 | Internal | Minimum | Liquidation | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Liquidation value		98.21%
Level 3 | Internal | Maximum | Discounted cash flow | Future policy benefits
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Lapse rate	12.00%	13.00%
Spread over LIBOR	1.27%	1.50%
Utilization rate	97.00%	96.00%
Withdrawal rate (greater than maximum range)	100.00%	100.00%
Mortality rate	14.00%	14.00%
Equity volatility curve	24.00%	25.00%
Level 3 | Internal | Maximum | Discounted cash flow | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Discount rate	14.85%	17.12%
Level 3 | Internal | Maximum | Liquidation | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Liquidation value		98.68%
Level 3 | Internal | Weighted Average | Discounted cash flow | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Discount rate	3.84%	4.71%
Level 3 | Internal | Weighted Average | Liquidation | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Liquidation value		98.64%
Level 3 | Internal | Fair Value, Measurements, Recurring
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Reinsurance recoverables	$ 242,381	$ 240,091
Future policy benefits	7,999,051	7,707,333
Level 3 | Internal | Fair Value, Measurements, Recurring | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Corporate securities	$ 128,030	$ 136,391