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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Equity Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	$ 5,242	$ 5,363	$ 5,247	$ 5,705
Purchases	0	0	0	0
Sales	0	0	0	(929)
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	6,180	5,109	6,180	5,109
Total gains (losses) (realized/unrealized):
Included in earnings	938	(254)	933	333
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	939	(254)	934	344
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	938	(254)	933	333
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	939	(254)	934	344
Equity Securities | Included in other comprehensive income (loss)
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
Equity Securities | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Other assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	27,136	0	8,059	0
Purchases	10,789	0	28,923	0
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	(4)	0	(6)	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	40,765	0	40,765	0
Total gains (losses) (realized/unrealized):
Included in earnings	2,844	0	3,789	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	2,840	0	3,784	0
Other assets | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	2,844	0	3,789	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	2,840	0	3,784	0
Other 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 assets | Included in other comprehensive income (loss)
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
Other assets | 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	539,123	339,744	302,814	239,911
Purchases	4,287	4,446	12,850	13,523
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	0	0	0
Other	0	0	0	21,895
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	488,335	412,099	488,335	412,099
Total gains (losses) (realized/unrealized):
Included in earnings	(55,075)	67,909	172,671	136,770
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(51,944)	70,279	178,844	142,329
Reinsurance recoverables | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(55,075)	67,909	172,671	136,770
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(51,944)	70,279	178,844	142,329
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
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0		0
Reinsurance recoverables | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Future policy benefits
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	(23,998,671)	(11,738,480)	(11,822,998)	(8,332,474)
Purchases	0	0	0	0
Sales	0	0	0	0
Issuances	(291,756)	(277,769)	(858,366)	(799,575)
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	(21,325,619)	(15,086,125)	(21,325,619)	(15,086,125)
Total gains (losses) (realized/unrealized):
Included in earnings	2,964,808	(3,069,876)	(8,644,255)	(5,954,076)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	2,776,482	(3,187,867)	(8,923,218)	(6,177,050)
Future policy benefits | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	2,964,808	(3,069,876)	(8,644,255)	(5,954,076)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	2,776,482	(3,187,867)	(8,923,218)	(6,177,050)
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
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	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	(226,072)	(121,102)	(196,892)	(42,350)
Purchases	0	0	0	0
Sales	0	0	0	0
Issuances	(42,423)	(33,107)	(92,937)	(98,781)
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	(303,060)	(153,935)	(303,060)	(153,935)
Total gains (losses) (realized/unrealized):
Included in earnings	(34,565)	274	(13,231)	(12,804)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(22,855)	2,610	9,727	(8,672)
Policyholders' account balances | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(34,565)	274	(13,231)	(12,804)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(22,855)	2,610	9,727	(8,672)
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
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0		0
Policyholders' account balances | 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	254	(630)	87	(2,530)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	414	(769)	(567)	(2,767)
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	1,683	515	(4,442)	3,429
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	1,432		(5,760)
Available-for-sale | Fixed maturities | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	59	50	56	188
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	12,216	9,380	10,547	8,132
Purchases	1,000	503	2,669	1,751
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	13,216	9,883	13,216	9,883
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 | Corporate securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	123,389	71,071	104,267	85,452
Purchases	13,775	10,340	28,948	17,653
Sales	7,775	0	(1,190)	0
Issuances	0	0	0	0
Settlements	(8,624)	(8,016)	(14,434)	(30,105)
Other	(7,775)	0	(7,775)	0
Transfers into Level 3	7,819	0	32,951	1,790
Transfers out of Level 3	(795)	0	(1,039)	(2,018)
Fair Value, end of period	137,391	73,034	137,391	73,034
Total gains (losses) (realized/unrealized):
Included in earnings	1,827	(361)	(4,337)	262
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	1,689	(769)	(6,353)	(2,765)
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	18,128	19,725	18,825	9,336
Purchases	1,899	0	8,044	44,273
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	(599)	(338)	(1,674)	(4,724)
Other	0	0	0	0
Transfers into Level 3	312	0	312	551
Transfers out of Level 3	0	0	(5,636)	(30,578)
Fair Value, end of period	19,909	19,683	19,909	19,683
Total gains (losses) (realized/unrealized):
Included in earnings	169	296	38	825
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	157	0	26	(2)
Trading | Fixed maturities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	4,301	4,044	4,464	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	5,021
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	4,666	3,960	4,666	3,960
Total gains (losses) (realized/unrealized):
Included in earnings	365	(84)	202	(1,061)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	371	(79)	218	(1,051)
Trading | Fixed maturities | 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
Trading | Fixed maturities | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	371	(79)	218	(1,051)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	371	(79)	218	(1,051)
Trading | Fixed maturities | Included in other comprehensive income (loss)
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
Trading | Fixed maturities | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	$ (6)	$ (5)	$ (16)	$ (10)