Fair Value of Assets and Liabilities (Quantitative Info for Level 3 Inputs) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Corporate securities	$ 68,391	$ 18,765
Future policy benefits	16,193,345	9,368,986
Policyholders’ account balances	6,031,569	5,353,596
Fair Value, Measurements, Recurring
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Future policy benefits	15,086,125	8,332,474
Policyholders’ account balances	$ 153,935	42,350
Level 3 | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Policyholder Age	45 years
Level 3 | Minimum | Future policy benefits
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Mortality rate	0.00%
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	$ 15,086,125	8,332,474
Policyholders’ account balances	$ 153,935	$ 42,350
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	0.16%	0.36%
Utilization rate	43.00%	50.00%
Withdrawal rate (greater than maximum range)	78.00%	78.00%
Mortality rate	0.00%	0.00%
Equity volatility curve	14.00%	18.00%
Level 3 | Internal | Minimum | Discounted cash flow | Policyholders' account balances
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Lapse rate	1.00%
Spread over LIBOR	0.16%
Equity volatility curve	13.00%
Level 3 | Internal | Minimum | Discounted cash flow | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Discount rate	7.00%	7.00%
Level 3 | Internal | Minimum | Market comparables | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
EBITDA multiples	6.7	6.7
Level 3 | Internal | Minimum | Liquidation | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Liquidation value		41.00%
Level 3 | Internal | Maximum | Discounted cash flow | Future policy benefits
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Lapse rate	18.00%	13.00%
Spread over LIBOR	1.46%	1.60%
Utilization rate	97.00%	97.00%
Withdrawal rate (greater than maximum range)	100.00%	100.00%
Mortality rate	15.00%	15.00%
Equity volatility curve	23.00%	22.00%
Level 3 | Internal | Maximum | Discounted cash flow | Policyholders' account balances
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Lapse rate	42.00%
Spread over LIBOR	1.46%
Equity volatility curve	25.00%
Level 3 | Internal | Maximum | Discounted cash flow | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Discount rate	20.00%	20.00%
Level 3 | Internal | Maximum | Market comparables | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
EBITDA multiples	6.7	6.7
Level 3 | Internal | Maximum | Liquidation | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Liquidation value		41.00%
Level 3 | Internal | Weighted Average | Discounted cash flow | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Discount rate	10.06%	11.30%
Level 3 | Internal | Weighted Average | Market comparables | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
EBITDA multiples	6.7	6.7
Level 3 | Internal | Weighted Average | Liquidation | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Liquidation value		41.00%
Level 3 | Internal | Fair Value, Measurements, Recurring | Future policy benefits
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Future policy benefits	$ 15,086,125	$ 8,332,474
Level 3 | Internal | Fair Value, Measurements, Recurring | Policyholders' account balances
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Policyholders’ account balances	153,935
Level 3 | Internal | Fair Value, Measurements, Recurring | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Corporate securities	17,812	18,609
Level 3 | Internal | Fair Value, Measurements, Recurring | Reinsurance recoverables
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Reinsurance recoverables	$ 412,099	$ 239,911