Fair Values of Financial Instruments - Schedule of Fair Value, Valuation Techniques and Significant Unobservable Inputs for Financial Instruments Categorized as Level 3 (Details) $ in Thousands	Dec. 31, 2021 USD ($) yr	Dec. 31, 2020 USD ($) yr
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Debt securities, available-for-sale	$ 9,068,946	$ 10,770,923
Derivatives, index options	101,622	132,821
Mortgage loans	8,469	0
Level 3
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Debt securities, available-for-sale	326,962	0
Derivatives, index options	101,622	132,821
Mortgage loans	513,246	348,175
Total assets	223,359	132,821
Total liabilities	150,630	167,553
Level 3 | Discounted cash flow
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Debt securities, available-for-sale	113,268
Mortgage loans	8,469
Level 3 | Broker prices
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Derivatives, index options	101,622	132,821
Level 3 | Deterministic cash flow model
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Policyholder account balances	142,761	161,351
Level 3 | Black-Scholes model
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Share based compensation	$ 7,869	$ 6,202
Discount rate | Level 3 | Discounted cash flow | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Debt Securities, available-for-sale, measurement input	0.0240
Discount rate | Level 3 | Discounted cash flow | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Debt Securities, available-for-sale, measurement input	0.0614
Discount rate | Level 3 | Discounted cash flow | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Debt Securities, available-for-sale, measurement input	0.0406
Implied volatility | Level 3 | Broker prices | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Derivatives, index options, measurement input	0.1176	0.1296
Implied volatility | Level 3 | Broker prices | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Derivatives, index options, measurement input	0.1654	0.5369
Implied volatility | Level 3 | Broker prices | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Derivatives, index options, measurement input	0.1455	0.2070
Measurement input spread | Level 3 | Discounted cash flow | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Mortgage loans, measurement input	0.0100
Measurement input spread | Level 3 | Discounted cash flow | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Mortgage loans, measurement input	0.0250
Projected option cost | Level 3 | Deterministic cash flow model | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Policyholder account balances, measurement input	0.0003	0.000
Projected option cost | Level 3 | Deterministic cash flow model | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Policyholder account balances, measurement input	0.1449	0.4504
Projected option cost | Level 3 | Deterministic cash flow model | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Policyholder account balances, measurement input	0.0265	0.0327
Expected term | Level 3 | Black-Scholes model | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Share based compensation, measurement input | yr	1.9	1.0
Expected term | Level 3 | Black-Scholes model | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Share based compensation, measurement input | yr	10	9.9
Expected volatility | Level 3 | Black-Scholes model
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Share based compensation, measurement input	0.3505	0.3347