Fair Value of Assets and Liabilities (Changes in Level 3 Assets and Liabilities) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	$ 5,705	$ 9,758
Purchases	0	0
Sales	(929)	(3,609)
Issuances	0	0
Settlements	0	0
Other	0	147
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	5,247	5,705	$ 9,758
Total gains (losses) (realized/unrealized):
Included in earnings	471	(591)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	482	(1,208)
Equity securities | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0
Equity securities | Other Income
Total gains (losses) (realized/unrealized):
Included in earnings	471	(591)	689
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	482	(1,208)	338
Equity securities | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	351
Equity securities | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Other invested assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	0	147
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	0	0
Other	0	(147)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	0	0	147
Total gains (losses) (realized/unrealized):
Included in earnings	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0
Other invested assets | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	(7)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	(7)
Other invested assets | Other Income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0
Other invested assets | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Other invested assets | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Short-term Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	0	87
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	0	(43)
Other	0	(24)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	0	0	87
Total gains (losses) (realized/unrealized):
Included in earnings	0	(20)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	(55)
Short-term Investments | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	(20)	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	(55)	0
Short-term Investments | Other Income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0
Short-term Investments | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Short-term Investments | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Cash equivalents
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	0	0
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	0	(13)
Other	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	0	0	0
Total gains (losses) (realized/unrealized):
Included in earnings	0	13
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0
Cash equivalents | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	13	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0
Cash equivalents | Other Income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0
Cash equivalents | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Cash equivalents | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Other assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	0	0
Purchases	7,618	0
Sales	0	0
Issuances	0	0
Settlements	0	0
Other	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	8,059	0	0
Total gains (losses) (realized/unrealized):
Included in earnings	441	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	441	0
Other assets | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	441	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	441	0	0
Other assets | Other Income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0
Other assets | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Other assets | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Reinsurance recoverables
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	239,911	244,006
Purchases	17,950	19,061
Sales	0	0
Issuances	0	0
Settlements	0	0
Other	21,896	5,601
Transfers into Level 3	0	0
Transfers out of Level 3	(47,006)	0
Fair Value, end of period	302,814	239,911	244,006
Total gains (losses) (realized/unrealized):
Included in earnings	70,063	(28,757)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	57,652	(19,962)
Reinsurance recoverables | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	70,063	(28,757)	(18,240)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	57,652	(19,962)	(10,303)
Reinsurance recoverables | Other Income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0
Reinsurance recoverables | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Reinsurance recoverables | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Future Policy Benefits
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	(8,332,474)	(8,151,902)
Purchases	0	0
Sales	0	0
Issuances	(1,080,566)	(1,024,486)
Settlements	0	0
Other	0	0
Transfers Into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	(11,822,998)	(8,332,474)	(8,151,902)
Total gains (losses) (realized/unrealized):
Included in earnings	(2,409,958)	843,914
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(2,710,167)	529,804
Future Policy Benefits | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(2,409,958)	843,914	552,047
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(2,710,167)	529,804	307,529
Future Policy Benefits | Other Income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0
Future Policy Benefits | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Future Policy Benefits | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Policyholders' account balances
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	(42,350)	0
Purchases	0	0
Sales	0	0
Issuances	(122,295)	(48,401)
Settlements	0	0
Other	0	0
Transfers Into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	(196,892)	(42,350)	0
Total gains (losses) (realized/unrealized):
Included in earnings	(32,247)	6,051
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(22,699)	6,051
Policyholders' account balances | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(32,247)	6,051	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(22,699)	6,051	0
Policyholders' account balances | Other Income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0
Policyholders' account balances | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Policyholders' account balances | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Available-for-sale | Fixed maturities | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(3,562)	(6,693)	(6,301)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(3,799)	(6,627)	(6,506)
Available-for-sale | Fixed maturities | Other Income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0
Available-for-sale | Fixed maturities | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	2,690	(5,194)	(3,410)
Available-for-sale | Fixed maturities | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	251	241	8,057
Available-for-sale | Fixed maturities | US government
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	8,132	5,237
Purchases	2,415	2,895
Sales	0	0
Issuances	0	0
Settlements	0	0
Other	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	10,547	8,132	5,237
Total gains (losses) (realized/unrealized):
Included in earnings	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0
Available-for-sale | Fixed maturities | Corporate securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	85,452	95,206
Purchases	61,563	15,268
Sales	0	(275)
Issuances	0	0
Settlements	(43,724)	(22,332)
Other	0	24
Transfers into Level 3	4,655	9,969
Transfers out of Level 3	(2,556)	(1,486)
Fair Value, end of period	104,267	85,452	95,206
Total gains (losses) (realized/unrealized):
Included in earnings	(1,123)	(10,922)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(3,797)	(6,627)
Available-for-sale | Fixed maturities | Structured securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	9,336	185,358
Purchases	44,273	84,810
Sales	0	(14,236)
Issuances	0	0
Settlements	(5,259)	(37,672)
Other	0	0
Transfers into Level 3	551	51,979
Transfers out of Level 3	(30,578)	(260,179)
Fair Value, end of period	18,825	9,336	185,358
Total gains (losses) (realized/unrealized):
Included in earnings	502	(724)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(2)	0
Trading | Fixed maturities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	0	0
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	0	0
Other	0	0
Transfers into Level 3	5,021	0
Transfers out of Level 3	0	0
Fair Value, end of period	4,464	0	0
Total gains (losses) (realized/unrealized):
Included in earnings	(557)	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(543)	0
Trading | Fixed maturities | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0
Trading | Fixed maturities | Other Income
Total gains (losses) (realized/unrealized):
Included in earnings	(543)	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(543)	0	0
Trading | Fixed maturities | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Trading | Fixed maturities | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	$ (14)	$ 0	$ 0