Fair Value of Assets and Liabilities (Changes in Level 3 Assets and Liabilities) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
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	(195)	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	5,616	10,617
Total gains (losses) (realized/unrealized):
Included in earnings	106	712
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	118	0
Equity Securities | 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
Equity Securities | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	106	712
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	118	0
Equity Securities | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0
Equity Securities | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	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
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
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0
Other invested assets | 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 invested assets | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0
Other invested assets | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	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	0
Other	0	(23)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	0	11
Total gains (losses) (realized/unrealized):
Included in earnings	0	(53)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0
Short-term investments | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	(53)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0
Short-term investments | 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
Short-term investments | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0
Short-term investments | Net investment income
Total gains (losses) (realized/unrealized):
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	239,911	244,006
Purchases	4,559	4,850
Sales	0	0
Issuances	0	0
Settlements	0	0
Other	21,896	(12,317)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	283,991	195,497
Total gains (losses) (realized/unrealized):
Included in earnings	17,625	(41,042)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	17,625	(38,617)
Reinsurance recoverables | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	17,625	(41,042)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	17,625	(38,617)
Reinsurance recoverables | 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
Reinsurance recoverables | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0
Reinsurance recoverables | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	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	0	0
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	0	0
Other	0	0
Transfers into Level 3	0	34,269
Transfers out of Level 3	0	0
Fair Value, end of period	0	34,163
Total gains (losses) (realized/unrealized):
Included in earnings	0	(106)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0
Receivables from parents and affiliates | 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
Receivables from parents and affiliates | 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
Receivables from parents and affiliates | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	(106)
Receivables from parents and affiliates | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	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	(257,341)	(254,920)
Settlements	0	0
Other	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	(9,316,905)	(6,578,210)
Total gains (losses) (realized/unrealized):
Included in earnings	(727,090)	1,828,612
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(790,926)	1,745,629
Future policy benefits | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(727,090)	1,828,612
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(790,926)	1,745,629
Future policy benefits | 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
Future policy benefits | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0
Future policy benefits | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	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	(30,246)	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	(80,579)	0
Total gains (losses) (realized/unrealized):
Included in earnings	(7,983)	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(7,983)	0
Policyholders' Account Balances | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(7,983)	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(7,983)	0
Policyholders' Account Balances | 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
Policyholders' Account Balances | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0
Policyholders' Account Balances | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0
Reinsurance payable
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		(129)
Transfers into Level 3		0
Transfers out of Level 3		0
Fair Value, end of period		(129)
Total gains (losses) (realized/unrealized):
Included in earnings		0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings		(12,317)
Reinsurance payable | 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		(12,317)
Reinsurance payable | Other income
Total gains (losses) (realized/unrealized):
Included in earnings		0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings		0
Reinsurance payable | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings		0
Reinsurance payable | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings		0
Available-for-sale | Fixed maturities | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(725)	(66)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(1,998)	(76)
Available-for-sale | Fixed maturities | 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
Available-for-sale | Fixed maturities | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	1,441	1,050
Available-for-sale | Fixed maturities | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	39	95
Available-for-sale | Fixed maturities | U.S. government
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	8,132	5,237
Purchases	647	645
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	8,779	5,882
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	3,226	151
Sales	0	(36)
Issuances	0	0
Settlements	(5,463)	(6,035)
Other	0	23
Transfers into Level 3	975	0
Transfers out of Level 3	0	(215)
Fair Value, end of period	84,800	90,273
Total gains (losses) (realized/unrealized):
Included in earnings	610	1,179
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(1,996)	(76)
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	63,810
Sales	0	0
Issuances	0	0
Settlements	(4,047)	(8,899)
Other	0	0
Transfers into Level 3	551	41,954
Transfers out of Level 3	0	(25,879)
Fair Value, end of period	50,258	256,244
Total gains (losses) (realized/unrealized):
Included in earnings	145	(100)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	$ (2)	$ 0