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	$ 15,997	$ 17,525
Purchases	0	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	15,991	17,039
Total gains (losses) (realized/unrealized):
Included in earnings	(6)	(486)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(6)	(486)
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	(6)	(486)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(6)	(486)
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	4	0
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	0	0
Other	0	0
Transfers into Level 3	0	9
Transfers out of Level 3	0	0
Fair Value, end of period	4	10
Total gains (losses) (realized/unrealized):
Included in earnings	0	1
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	2
Other invested assets | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	1
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	2
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	1,339
Purchases	0	3,400
Sales	0	0
Issuances	0	0
Settlements	0	(3,513)
Other	0	(14)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	0	1,194
Total gains (losses) (realized/unrealized):
Included in earnings	0	(18)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	(18)
Short-term Investments | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	(18)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	(18)
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	5,600,008	5,457,649
Purchases	235,378	219,457
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	6,468,704	4,214,114
Total gains (losses) (realized/unrealized):
Included in earnings	633,318	(1,462,992)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	677,444	(1,409,320)
Reinsurance recoverables | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	633,318	(1,462,992)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	677,444	(1,409,320)
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	9,261	0
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	(1,580)	0
Other	0	0
Transfers into Level 3	0	6,551
Transfers out of Level 3	0	0
Fair Value, end of period	7,792	6,531
Total gains (losses) (realized/unrealized):
Included in earnings	111	(20)
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	(20)
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	0
Receivables from parents and affiliates | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	111	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	(233,435)	(226,345)
Settlements	0	0
Other	0	0
Transfers Into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	(6,459,377)	(4,191,373)
Total gains (losses) (realized/unrealized):
Included in earnings	(637,102)	1,487,555
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(681,227)	1,433,872
Future policy benefits | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(637,102)	1,487,555
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(681,227)	1,433,872
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	(13,015)	(46,651)
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	(6,507)	2,122
Other	0	0
Transfers Into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	(53,136)	(39,516)
Total gains (losses) (realized/unrealized):
Included in earnings	(33,614)	5,013
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(33,614)	5,013
Policyholders' account balances | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(33,614)	5,013
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(33,614)	5,013
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
Other liabilities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period		0
Purchases		8,825
Sales		0
Issuances		0
Settlements		0
Other		0
Transfers Into Level 3		0
Transfers out of Level 3		0
Fair Value, end of period		(15,955)
Total gains (losses) (realized/unrealized):
Included in earnings		(24,780)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings		(24,780)
Other liabilities | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings		(24,780)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings		(24,780)
Other liabilities | Other income
Total gains (losses) (realized/unrealized):
Included in earnings		0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings		0
Other liabilities | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings		0
Other liabilities | 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	(2,402)	68
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(3,163)	(26)
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	164	914
Available-for-sale | Fixed maturities | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	99	77
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	2,372	2,365
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	32,188	21,569
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 bonds
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	0
Fair Value, end of period	164	166
Total gains (losses) (realized/unrealized):
Included in earnings	5	(8)
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	1,331	1,022
Sales	(28)	0
Issuances	0	0
Settlements	(7,097)	(4,570)
Other	1	15
Transfers into Level 3	7,577	0
Transfers out of Level 3	0	(209)
Fair Value, end of period	54,960	72,615
Total gains (losses) (realized/unrealized):
Included in earnings	(3,412)	936
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(3,163)	(26)
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	190
Sales	(1)	0
Issuances	0	0
Settlements	(3,979)	(3,195)
Other	0	0
Transfers into Level 3	75,960	13,513
Transfers out of Level 3	0	(26,794)
Fair Value, end of period	79,804	94,873
Total gains (losses) (realized/unrealized):
Included in earnings	1,268	131
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	$ 0	$ 0