Fair Value of Assets and Liabilities (Changes in Level 3 Assets and Liabilities) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	$ 15,991	$ 17,039	$ 15,997	$ 17,525
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	0
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	17,105	16,625	17,105	16,625
Total gains (losses) (realized/unrealized):
Included in earnings	1,114	(414)	1,108	(900)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	1,114	(414)	1,108	(900)
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	1,114	(414)	1,108	(900)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	1,114	(414)	1,108	(900)
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	10	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	0	0	0
Fair Value, end of period	4	5	4	5
Total gains (losses) (realized/unrealized):
Included in earnings	0	(5)	0	(4)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	(5)	0	(4)
Other invested assets | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	(5)	0	(4)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	(5)	0	(4)
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	0	1,194	0	1,339
Purchases	463	1,870	463	5,270
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	(369)	(2,731)	(369)	(6,244)
Other	0	0	0	(14)
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	94	333	94	333
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		0
Purchases		2,550		2,550
Sales		0		0
Issuances		0		0
Settlements		(1,986)		(1,986)
Other		0		0
Transfers into Level 3		0		0
Transfers out of Level 3		0		0
Fair Value, end of period		564		564
Total gains (losses) (realized/unrealized):
Included in earnings		0		0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings		0		0
Reinsurance recoverables
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	6,468,704	4,214,114	5,600,008	5,457,649
Purchases	244,013	221,324	479,391	440,781
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	8,485,905	3,943,881	8,485,905	3,943,881
Total gains (losses) (realized/unrealized):
Included in earnings	1,773,188	(491,557)	2,406,506	(1,954,549)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	1,833,209	(441,257)	2,504,883	(1,844,015)
Reinsurance recoverables | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	1,773,188	(491,557)	2,406,506	(1,954,549)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	1,833,209	(441,257)	2,504,883	(1,844,015)
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	7,792	6,531	9,261	0
Purchases	0	0	0	0
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	(1,579)	0	(3,159)	0
Other	0	0	0	0
Transfers into Level 3	0	0	0	6,551
Transfers out of Level 3	0	(6,531)	0	(6,531)
Fair Value, end of period	6,295	0	6,295	0
Total gains (losses) (realized/unrealized):
Included in earnings	82	0	193	(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	82	0	193	0
Future policy benefits
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	(6,459,377)	(4,191,373)	(5,588,840)	(5,452,583)
Purchases	0	0	0	0
Sales	0	0	0	0
Issuances	(242,067)	(228,243)	(475,502)	(454,588)
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	(8,476,541)	(3,916,973)	(8,476,541)	(3,916,973)
Total gains (losses) (realized/unrealized):
Included in earnings	(1,775,097)	502,643	(2,412,199)	1,990,198
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(1,836,960)	459,185	(2,510,576)	1,879,579
Future policy benefits | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(1,775,097)	502,643	(2,412,199)	1,990,198
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(1,836,960)	459,185	(2,510,576)	1,879,579
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	(53,136)	(39,516)	(13,015)	(46,651)
Purchases	0	0	0	0
Sales	0	0	0	0
Issuances	(41,906)	0	(48,413)	0
Settlements	0	5,429	0	7,551
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	(786,969)	(41,946)	(786,969)	(41,946)
Total gains (losses) (realized/unrealized):
Included in earnings	(691,927)	(7,859)	(725,541)	(2,846)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(691,376)	(7,860)	(724,989)	(2,847)
Policyholders' account balances | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(691,927)	(7,859)	(725,541)	(2,846)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(691,376)	(7,860)	(724,989)	(2,847)
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		(15,955)		0
Purchases		8,880		17,705
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		(17,610)		(17,610)
Total gains (losses) (realized/unrealized):
Included in earnings		(10,535)		(35,315)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings		(10,590)		(35,231)
Other liabilities | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings		(10,535)		(35,315)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings		(10,590)		(35,231)
Other liabilities | Other income
Total gains (losses) (realized/unrealized):
Included in earnings		0		0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings		0		0
Other liabilities | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings		0		0
Other liabilities | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings		0		0
Available-for-sale | Fixed maturities | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(665)	(303)	(3,067)	(235)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	(49)	(3,163)	(75)
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	678	(1,620)	842	(706)
Available-for-sale | Fixed maturities | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	264	86	363	163
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	32,188	21,569	29,816	19,204
Purchases	2,204	2,842	4,576	5,207
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	34,392	24,411	34,392	24,411
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	164	166	0	0
Purchases	0		0	0
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	0	0	0
Other	0	0	0	174
Transfers into Level 3	0	0	159	0
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	165	160	165	160
Total gains (losses) (realized/unrealized):
Included in earnings	1	(6)	6	(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	54,960	72,615	56,588	75,421
Purchases	791	3,125	2,122	4,147
Sales	(25)	(201)	(53)	(201)
Issuances	0	0	0	0
Settlements	(2,584)	(15,501)	(9,681)	(20,071)
Other	(1)	(1)	0	14
Transfers into Level 3	639	4,028	8,216	4,028
Transfers out of Level 3	0	0	0	(209)
Fair Value, end of period	54,014	62,418	54,014	62,418
Total gains (losses) (realized/unrealized):
Included in earnings	234	(1,647)	(3,178)	(711)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	(49)	(3,163)	(75)
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	79,804	94,873	6,556	111,028
Purchases	0	10,648	0	10,838
Sales	(1)	(196)	(2)	(196)
Issuances	0	0	0	0
Settlements	(177)	(4,871)	(4,156)	(8,066)
Other	0	0	0	0
Transfers into Level 3	1,700	0	77,660	13,513
Transfers out of Level 3	(77,071)	(80,609)	(77,071)	(107,403)
Fair Value, end of period	4,297	19,661	4,297	19,661
Total gains (losses) (realized/unrealized):
Included in earnings	42	(184)	1,310	(53)
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	0		0
Purchases	0		0
Sales	0		0
Issuances	0		0
Settlements	0		0
Other	0		0
Transfers into Level 3	751		751
Transfers out of Level 3	0		0
Fair Value, end of period	605		605
Total gains (losses) (realized/unrealized):
Included in earnings	(146)		(146)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(146)		(146)
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	(146)		(146)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(146)		(146)
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