Net Investment Income (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Net Investment Income [Line Items]
Gross investment income	$ 181,457	$ 144,430	$ 511,789	$ 409,187
Investment expense	(1,606)	(1,780)	(5,174)	(6,343)
Net investment income	179,851	142,650	506,615	402,844
Fixed maturity securities, including cash and cash equivalents and loans receivable
Net Investment Income [Line Items]
Gross investment income	93,031	97,080	284,704	330,941
Investment funds
Net Investment Income [Line Items]
Investment funds	69,292	18,235	169,538	1,260
Arbitrage trading account
Net Investment Income [Line Items]
Gross investment income	7,187	19,543	30,176	51,985
Equity securities
Net Investment Income [Line Items]
Gross investment income	3,485	7,666	5,517	18,807
Real estate
Net Investment Income [Line Items]
Gross investment income	$ 8,462	$ 1,907	$ 21,854	$ 6,194

Amount before accretion (amortization) of purchase discount (premium) of interest income and dividend income on nonoperating securities.

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Amount of expenses related to the generation of investment income.

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Amount after accretion (amortization) of discount (premium), and investment expense, of interest income and dividend income on nonoperating securities.

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Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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