Fair Values of Financial Instruments - Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	$ 9,068,946	$ 10,770,923
Debt securities, trading	1,077,438	0
Equity securities	28,217	17,744
Mortgage loans	8,469	0
Derivatives, index options	101,622	132,821
Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	9,068,946	10,770,923
Debt securities, trading	1,077,438
Equity securities	28,217	17,744
Mortgage loans	8,469
Derivatives, index options	101,622	132,821
Total assets	10,284,692	10,921,488
Policyholder account balances	142,761	161,351
Other liabilities	(76,856)	6,202
Total liabilities	$ 65,905	167,553
Percent of total	100.00%
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	$ 0	0
Debt securities, trading	0
Equity securities	23,795	17,744
Mortgage loans	0	0
Derivatives, index options	0	0
Level 1 | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	0	0
Debt securities, trading	0
Equity securities	23,795	17,744
Mortgage loans	0
Derivatives, index options	0	0
Total assets	23,795	17,744
Policyholder account balances	0	0
Other liabilities	0	0
Total liabilities	$ 0	0
Percent of total	0.20%
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	$ 8,741,984	10,770,923
Debt securities, trading	1,002,616
Equity securities	4,422	0
Mortgage loans	0	0
Derivatives, index options	0	0
Level 2 | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	8,741,984	10,770,923
Debt securities, trading	1,002,616
Equity securities	4,422	0
Mortgage loans	0
Derivatives, index options	0	0
Total assets	9,749,022	10,770,923
Policyholder account balances	0	0
Other liabilities	(84,725)	0
Total liabilities	$ (84,725)	0
Percent of total	94.80%
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	$ 326,962	0
Debt securities, trading	74,822
Equity securities	0	0
Mortgage loans	513,246	348,175
Derivatives, index options	101,622	132,821
Total assets	223,359	132,821
Total liabilities	150,630	167,553
Level 3 | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	326,962	0
Debt securities, trading	74,822
Equity securities	0	0
Mortgage loans	8,469
Derivatives, index options	101,622	132,821
Total assets	511,875	132,821
Policyholder account balances	142,761	161,351
Other liabilities	7,869	6,202
Total liabilities	$ 150,630	$ 167,553
Percent of total	5.00%
Priced by third-party vendors | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	$ 8,955,678
Debt securities, trading	1,077,438
Equity securities	28,217
Mortgage loans	0
Derivatives, index options	101,622
Priced by third-party vendors | Level 1 | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	0
Debt securities, trading	0
Equity securities	23,795
Mortgage loans	0
Derivatives, index options	0
Priced by third-party vendors | Level 2 | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	8,741,984
Debt securities, trading	1,002,616
Equity securities	4,422
Mortgage loans	0
Derivatives, index options	0
Priced by third-party vendors | Level 3 | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	213,694
Debt securities, trading	74,822
Equity securities	0
Mortgage loans	0
Derivatives, index options	101,622
Priced internally | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	113,268
Debt securities, trading	0
Equity securities	0
Mortgage loans	8,469
Derivatives, index options	0
Priced internally | Level 1 | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	0
Debt securities, trading	0
Equity securities	0
Mortgage loans	0
Derivatives, index options	0
Priced internally | Level 2 | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	0
Debt securities, trading	0
Equity securities	0
Mortgage loans	0
Derivatives, index options	0
Priced internally | Level 3 | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	113,268
Debt securities, trading	0
Equity securities	0
Mortgage loans	8,469
Derivatives, index options	$ 0