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	$ 15,997	$ 17,525
Purchases	0	0
Sales	(7,767)	(75)
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	9,898	15,997	$ 17,525
Total gains (losses) (realized/unrealized):
Included in earnings	1,668	(1,453)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	1,534	(1,453)
Equity securities | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	1,707
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	1,668	(1,453)	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	1,534	(1,453)	2,345
Equity securities | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	(38)
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	4	0
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	0	0
Other	0	0
Transfers into Level 3	0	18
Transfers out of Level 3	0	(9)
Fair Value, end of period	4	4	0
Total gains (losses) (realized/unrealized):
Included in earnings	0	(5)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	(5)
Other Invested Assets | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	(5)	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	(5)	0
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	1,339
Purchases	1,388	11,106
Sales	0	(73)
Issuances	0	0
Settlements	(1,388)	(12,311)
Other	0	(14)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	0	0	1,339
Total gains (losses) (realized/unrealized):
Included in earnings	0	(47)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	(19)
Short-term Investments | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	(47)	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	(19)	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 and cash equivalents
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	0	0
Purchases	0	4,987
Sales	0	(465)
Issuances	0	0
Settlements	0	(4,266)
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	(256)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0
Cash and cash equivalents | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	(256)	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0
Cash and 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 and cash equivalents | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Cash and cash equivalents | 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	5,600,008	5,457,649
Purchases	1,003,300	924,384
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	8,539,671	5,600,008	5,457,649
Total gains (losses) (realized/unrealized):
Included in earnings	1,936,363	(782,025)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	2,142,421	(573,853)
Reinsurance recoverables | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	1,936,363	(782,025)	(158,623)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	2,142,421	(573,853)	(315,998)
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
Receivables from Parent and Affiliates
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	9,261	0
Purchases	0	9,719
Sales	0	0
Issuances	0	0
Settlements	(6,316)	(525)
Other	0	0
Transfers into Level 3	0	6,551
Transfers out of Level 3	0	(6,531)
Fair Value, end of period	3,135	9,261	0
Total gains (losses) (realized/unrealized):
Included in earnings	190	47
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0
Receivables from Parent and Affiliates | 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
Receivables from Parent and Affiliates | 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
Receivables from Parent and Affiliates | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	(20)	0
Receivables from Parent and Affiliates | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	190	67	0
Future policy benefits
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	(5,588,840)	(5,452,583)
Purchases	0	0
Sales	0	0
Issuances	(995,403)	(916,518)
Settlements	0	0
Other	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	(8,529,566)	(5,588,840)	(5,452,583)
Total gains (losses) (realized/unrealized):
Included in earnings	(1,945,323)	780,261
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(2,151,380)	572,088
Future policy benefits | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(1,945,323)	780,261	463,432
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(2,151,380)	572,088	313,532
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	(13,015)	(46,651)
Purchases	0	0
Sales	0	0
Issuances	(183,419)	0
Settlements	0	9,231
Other	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	(962,351)	(13,015)	(46,651)
Total gains (losses) (realized/unrealized):
Included in earnings	(765,917)	24,405
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(759,661)	24,405
Policyholders' account balances | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(765,917)	24,405	(30,991)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(759,661)	24,405	(30,991)
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	(8,198)	(1,600)	2,001
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(8,467)	(1,944)	(2,736)
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	3,615	(6,015)	(1,588)
Available-for-sale | Fixed maturities | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	680	418	270
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	29,816	19,204
Purchases	8,855	10,679
Sales	0	(67)
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	38,671	29,816	19,204
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 | Foreign government
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	174
Transfers into Level 3	159	0
Transfers out of Level 3	0	(159)
Fair Value, end of period	163	0	0
Total gains (losses) (realized/unrealized):
Included in earnings	4	(15)
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	56,588	75,421
Purchases	4,226	13,573
Sales	(81)	(215)
Issuances	0	0
Settlements	(18,884)	(39,459)
Other	0	15
Transfers into Level 3	13,463	18,877
Transfers out of Level 3	0	(4,982)
Fair Value, end of period	50,083	56,588	75,421
Total gains (losses) (realized/unrealized):
Included in earnings	(5,229)	(6,642)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(8,467)	(1,944)
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	6,556	111,028
Purchases	0	31,067
Sales	(130)	(10,844)
Issuances	0	0
Settlements	(6,336)	(10,216)
Other	0	0
Transfers into Level 3	77,660	13,513
Transfers out of Level 3	(77,071)	(127,452)
Fair Value, end of period	2,001	6,556	$ 111,028
Total gains (losses) (realized/unrealized):
Included in earnings	1,322	(540)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0
Trading | Fixed maturities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	0
Purchases	0
Sales	0
Issuances	0
Settlements	0
Other	0
Transfers into Level 3	751
Transfers out of Level 3	0
Fair Value, end of period	668	$ 0
Total gains (losses) (realized/unrealized):
Included in earnings	(83)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(83)
Trading | Fixed maturities | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0
Trading | Fixed maturities | Other Income
Total gains (losses) (realized/unrealized):
Included in earnings	(83)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(83)
Trading | Fixed maturities | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0
Trading | Fixed maturities | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	$ 0