Fair Value of Assets and Liabilities (Changes in Level 3 Assets and Liabilities) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	$ 17,105	$ 16,625	$ 15,997	$ 17,525
Purchases	0	0	0	0
Sales	0	(75)	0	(75)
Issuances	0	0	0	0
Settlements	0	0	0	0
Other	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	17,371	16,327	17,371	16,327
Total gains (losses) (realized/unrealized):
Included in earnings	266	(223)	1,374	(1,123)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	266	(222)	1,374	(1,123)
Equity securities | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Equity securities | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	266	(223)	1,374	(1,123)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	266	(222)	1,374	(1,123)
Equity securities | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Equity securities | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Other invested assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	4	5	4	0
Purchases	0	0	0	0
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	0	0	0
Other	0	0	0	0
Transfers into Level 3	0	0	0	9
Transfers out of Level 3	0	(9)	0	(9)
Fair Value, end of period	4	0	4	0
Total gains (losses) (realized/unrealized):
Included in earnings	0	4	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	4	0	0
Other invested assets | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	4	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	4	0	0
Other invested assets | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Other invested assets | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Other invested assets | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Short-term Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	94	333	0	1,339
Purchases	606	5,440	1,069	10,710
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	(244)	(5,316)	(613)	(11,560)
Other	0	(1)	0	(15)
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	456	456	456	456
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	(18)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	(1)	0	(19)
Short-term Investments | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	(18)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	(1)	0	(19)
Short-term Investments | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Short-term Investments | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Short-term Investments | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Cash equivalents
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	0	564	0	0
Purchases	0	0	0	2,550
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	(564)	0	(2,550)
Other	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	0	0	0	0
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Cash equivalents | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Cash equivalents | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Cash equivalents | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Cash equivalents | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Reinsurance recoverables
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	8,485,905	3,943,881	5,600,008	5,457,649
Purchases	259,782	224,620	739,173	665,401
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	0	0	0
Other	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	11,313,614	2,958,093	11,313,614	2,958,093
Total gains (losses) (realized/unrealized):
Included in earnings	2,567,927	(1,210,408)	4,974,433	(3,164,957)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	2,653,797	(1,174,501)	5,127,527	(3,000,498)
Reinsurance recoverables | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	2,567,927	(1,210,408)	4,974,433	(3,164,957)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	2,653,797	(1,174,501)	5,127,527	(3,000,498)
Reinsurance recoverables | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Reinsurance recoverables | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Reinsurance recoverables | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Receivables from parents and affiliates
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	6,295	0	9,261	0
Purchases	0	0	0	0
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	(1,578)	0	(4,737)	0
Other	0	0	0	0
Transfers into Level 3	0	0	0	6,551
Transfers out of Level 3	0	0	0	(6,531)
Fair Value, end of period	4,682	0	4,682	0
Total gains (losses) (realized/unrealized):
Included in earnings	(35)	0	158	(20)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Receivables from parents and affiliates | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Receivables from parents and affiliates | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	(20)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Receivables from parents and affiliates | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Receivables from parents and affiliates | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	(35)	0	158	0
Future policy benefits
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	(8,476,541)	(3,916,973)	(5,588,840)	(5,452,583)
Purchases	0	0	0	0
Sales	0	0	0	0
Issuances	(257,739)	(231,467)	(733,241)	(686,055)
Settlements	0	0	0	0
Other	0	0	0	0
Transfers Into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	(11,302,531)	(2,908,324)	(11,302,531)	(2,908,324)
Total gains (losses) (realized/unrealized):
Included in earnings	(2,568,251)	1,240,116	(4,980,450)	3,230,314
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(2,655,925)	1,204,459	(5,133,545)	3,065,835
Future policy benefits | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(2,568,251)	1,240,116	(4,980,450)	3,230,314
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(2,655,925)	1,204,459	(5,133,545)	3,065,835
Future policy benefits | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Future policy benefits | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Future policy benefits | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Policyholders' account balances
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	(786,969)	(41,946)	(13,015)	(46,651)
Purchases	0	0	0	0
Sales	0	0	0	0
Issuances	(115,012)	0	(163,425)	0
Settlements	0	2,940	0	10,491
Other	0	0	0	0
Transfers Into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	(875,975)	(60,847)	(875,975)	(60,847)
Total gains (losses) (realized/unrealized):
Included in earnings	26,006	(21,841)	(699,535)	(24,687)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	35,117	(21,841)	(689,872)	(24,688)
Policyholders' account balances | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	26,006	(21,841)	(699,535)	(24,687)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	35,117	(21,841)	(689,872)	(24,688)
Policyholders' account balances | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Policyholders' account balances | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Policyholders' account balances | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Other liabilities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	0	(17,610)	0	0
Purchases	0	8,778	0	26,483
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	0	0	0
Other	0	0	0	0
Transfers Into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	0	(41,333)	0	(41,333)
Total gains (losses) (realized/unrealized):
Included in earnings	0	(32,501)	0	(67,816)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	(32,750)	0	(67,796)
Other liabilities | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	(32,501)	0	(67,816)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	(32,750)	0	(67,796)
Other liabilities | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Other liabilities | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Other liabilities | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Available-for-sale | Fixed maturities | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(1,549)	(809)	(4,616)	(1,044)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(1,731)	(1,310)	(4,893)	(1,385)
Available-for-sale | Fixed maturities | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Available-for-sale | Fixed maturities | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	1,406	(2,675)	2,248	(3,382)
Available-for-sale | Fixed maturities | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	144	143	507	307
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	34,392	24,411	29,816	19,204
Purchases	1,847	935	6,423	6,142
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	0	0	0
Other	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	36,239	25,346	36,239	25,346
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Available-for-sale | Fixed maturities | Foreign government bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	165	160	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	0	0	0
Other	0	(1)	0	173
Transfers into Level 3	0	0	159	0
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	164	159	164	159
Total gains (losses) (realized/unrealized):
Included in earnings	(1)	0	5	(14)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	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	54,014	62,418	56,588	75,421
Purchases	796	669	2,918	4,816
Sales	(28)	0	(81)	(201)
Issuances	0	0	0	0
Settlements	(1,158)	(12,767)	(10,839)	(32,838)
Other	0	0	0	14
Transfers into Level 3	5,247	0	13,463	4,028
Transfers out of Level 3	0	(3,936)	0	(4,145)
Fair Value, end of period	58,857	43,467	58,857	43,467
Total gains (losses) (realized/unrealized):
Included in earnings	(14)	(2,917)	(3,192)	(3,628)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(1,731)	(1,310)	(4,893)	(1,385)
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	4,297	19,661	6,556	111,028
Purchases	0	20,229	0	31,067
Sales	(101)	(10,648)	(103)	(10,844)
Issuances	0	0	0	0
Settlements	(178)	(2,138)	(4,334)	(10,204)
Other	0	0	0	0
Transfers into Level 3	0	0	77,660	13,513
Transfers out of Level 3	0	0	(77,071)	(107,403)
Fair Value, end of period	4,034	26,680	4,034	26,680
Total gains (losses) (realized/unrealized):
Included in earnings	16	(424)	1,326	(477)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	$ 0	0	$ 0
Trading | Fixed maturities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	605		0
Purchases	0		0
Sales	0		0
Issuances	0		0
Settlements	0		0
Other	0		0
Transfers into Level 3	0		751
Transfers out of Level 3	0		0
Fair Value, end of period	593		593
Total gains (losses) (realized/unrealized):
Included in earnings	(12)		(158)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(12)		(158)
Trading | Fixed maturities | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0		0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0		0
Trading | Fixed maturities | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	(12)		(158)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(12)		(158)
Trading | Fixed maturities | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0		0
Trading | Fixed maturities | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	$ 0		$ 0