Investments - Summary of Rating of Debt securities (Parenthetical) (Detail) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities	$ 14,651,254	$ 16,061,560
BB / Ba
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities	124,400
B
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities	173,700
CCC
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities	21,200
CC
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities	500
Below CC
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities	2,900
Not rated securities
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities	$ 102,800