Fair Value of Financial Instruments - Assets and Liabilities Measured on Recurring Basis (Details) - USD ($)	3 Months Ended	6 Months Ended
	Jun. 30, 2022	Jun. 30, 2022	Dec. 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	$ 8,160,952,000	$ 8,160,952,000	$ 9,068,946,000
Debt securities, trading	909,647,000	909,647,000	1,077,438,000
Equity securities	22,121,000	22,121,000	28,217,000
Mortgage loans	18,738,000	18,738,000	8,469,000
Derivatives, index options	6,071,000	6,071,000	101,622,000
Transfer from Level 2 to Level 3 for debt securities available for sale	0	0
Transfer from level 2 to level 3 for liabilities	0
Fair Value, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	8,160,952,000	8,160,952,000	9,068,946,000
Debt securities, trading	909,647,000	909,647,000	1,077,438,000
Equity securities	22,121,000	22,121,000	28,217,000
Mortgage loans	18,738,000	18,738,000	8,469,000
Derivatives, index options	6,071,000	6,071,000	101,622,000
Total assets	9,117,529,000	9,117,529,000	10,284,692,000
Policyholder account balances	45,342,000	45,342,000	142,761,000
Other liabilities	(261,282,000)	(261,282,000)	(76,856,000)
Total liabilities	$ (215,940,000)	$ (215,940,000)	$ 65,905,000
Percent of total	100.00%	100.00%	100.00%
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	$ 0	$ 0	$ 0
Debt securities, trading	0	0	0
Equity securities	18,433,000	18,433,000	23,795,000
Derivatives, index options	0	0	0
Level 1 | Fair Value, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	0	0	0
Debt securities, trading	0	0	0
Equity securities	18,433,000	18,433,000	23,795,000
Mortgage loans	0	0	0
Derivatives, index options	0	0	0
Total assets	18,433,000	18,433,000	23,795,000
Policyholder account balances	0	0	0
Other liabilities	0	0	0
Total liabilities	$ 0	$ 0	$ 0
Percent of total	0.20%	0.20%	0.20%
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	$ 7,786,995,000	$ 7,786,995,000	$ 8,741,984,000
Debt securities, trading	809,878,000	809,878,000	1,002,616,000
Equity securities	3,688,000	3,688,000	4,422,000
Derivatives, index options	0	0	0
Level 2 | Fair Value, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	7,786,995,000	7,786,995,000	8,741,984,000
Debt securities, trading	809,878,000	809,878,000	1,002,616,000
Equity securities	3,688,000	3,688,000	4,422,000
Mortgage loans	0	0	0
Derivatives, index options	0	0	0
Total assets	8,600,561,000	8,600,561,000	9,749,022,000
Policyholder account balances	0	0	0
Other liabilities	(264,080,000)	(264,080,000)	(84,725,000)
Total liabilities	$ (264,080,000)	$ (264,080,000)	$ (84,725,000)
Percent of total	94.30%	94.30%	94.80%
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	$ 373,957,000	$ 373,957,000	$ 326,962,000
Debt securities, trading	99,769,000	99,769,000	74,822,000
Equity securities	0	0	0
Derivatives, index options	6,071,000	6,071,000	101,622,000
Total assets	69,781,000	69,781,000	223,359,000
Total liabilities	54,674,000	54,674,000	150,630,000
Level 3 | Fair Value, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	373,957,000	373,957,000	326,962,000
Debt securities, trading	99,769,000	99,769,000	74,822,000
Equity securities	0	0	0
Mortgage loans	18,738,000	18,738,000	8,469,000
Derivatives, index options	6,071,000	6,071,000	101,622,000
Total assets	498,535,000	498,535,000	511,875,000
Policyholder account balances	45,342,000	45,342,000	142,761,000
Other liabilities	2,798,000	2,798,000	7,869,000
Total liabilities	$ 48,140,000	$ 48,140,000	$ 150,630,000
Percent of total	5.50%	5.50%	5.00%
Priced by third-party vendors | Fair Value, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	$ 8,115,980,000	$ 8,115,980,000	$ 8,955,678,000
Debt securities, trading	909,647,000	909,647,000	1,077,438,000
Equity securities	22,121,000	22,121,000	28,217,000
Mortgage loans	0	0	0
Derivatives, index options	6,071,000	6,071,000	101,622,000
Priced by third-party vendors | Level 1 | Fair Value, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	0	0	0
Debt securities, trading	0	0	0
Equity securities	18,433,000	18,433,000	23,795,000
Mortgage loans	0	0	0
Derivatives, index options	0	0	0
Priced by third-party vendors | Level 2 | Fair Value, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	7,786,995,000	7,786,995,000	8,741,984,000
Debt securities, trading	809,878,000	809,878,000	1,002,616,000
Equity securities	3,688,000	3,688,000	4,422,000
Mortgage loans	0	0	0
Derivatives, index options	0	0	0
Priced by third-party vendors | Level 3 | Fair Value, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	328,985,000	328,985,000	213,694,000
Debt securities, trading	99,769,000	99,769,000	74,822,000
Equity securities	0	0	0
Mortgage loans	0	0	0
Derivatives, index options	6,071,000	6,071,000	101,622,000
Priced internally | Fair Value, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	44,972,000	44,972,000	113,268,000
Debt securities, trading	0	0	0
Equity securities	0	0	0
Mortgage loans	18,738,000	18,738,000	8,469,000
Derivatives, index options	0	0	0
Priced internally | Level 1 | Fair Value, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	0	0	0
Debt securities, trading	0	0	0
Equity securities	0	0	0
Mortgage loans	0	0	0
Derivatives, index options	0	0	0
Priced internally | Level 2 | Fair Value, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	0	0	0
Debt securities, trading	0	0	0
Equity securities	0	0	0
Mortgage loans	0	0	0
Derivatives, index options	0	0	0
Priced internally | Level 3 | Fair Value, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	44,972,000	44,972,000	113,268,000
Debt securities, trading	0	0	0
Equity securities	0	0	0
Mortgage loans	18,738,000	18,738,000	8,469,000
Derivatives, index options	$ 0	$ 0	$ 0