Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Other Investments	$ 690,000	$ 595,000
Credit valuation adjustment included in fair value of credit derivative liabilities	32	19
Fair value of derivative liabilities	93,000
Derivative liabilities	$ 95,000	$ 114,000
Weighted average discounted rate of estimated future premium payments to be paid by the VIEs	2.20%	2.20%
Number of Credit Risk Derivatives Held	1
Fixed Income Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Percentage of investment portfolio valued using dealer quotes	6.00%	2.00%
Asset-backed Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Coupon rate	5.97%	5.97%
Minimum [Member] \| Fixed Income Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Percentage of investment portfolio valued using internal valuation models	4.00%	3.00%
Maximum [Member] \| Fixed Income Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Percentage of investment portfolio valued using external pricing services	90.00%	95.00%
Variable Interest Entity, Primary Beneficiary [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fair value of derivative liabilities	$ 0
Derivative liabilities	$ 1,940,000	$ 1,835,000
Weighted average discounted rate of estimated future premium payments to be paid by the VIEs	3.00%	2.40%
Real Estate [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Other Investments	$ 33,000	$ 16,000
Hedge Funds, Multi-strategy [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Other Investments	216,000	196,000
Interest Rate Contract [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Other Investments	78,000	78,000
Illiquid Investments [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Other Investments	$ 88,000	$ 65,000

Weighted average discounted rate of estimated future premium payments to be paid by the VIEs.

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Investment portfolio valued using dealer quotes.

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Amount of credit risk valuation adjustment to derivative liabilities to properly reflect the credit quality of the entity.

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Number of credit risk derivative instruments held.

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Amount of investments classified as other.

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