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Changes in Level 3 Investments Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Fair Value Disclosures [Abstract]
Beginning balance	$ 0	$ 3,787	$ 0	$ 4,571
Included in accumulated other comprehensive income (loss)	$ 0	$ 3	$ 0	$ 10
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Asset, Gain (Loss), Statement of Other Comprehensive Income or Comprehensive Income [Extensible Enumeration]	Other Comprehensive Income (Loss), Net of Tax	Other Comprehensive Income (Loss), Net of Tax	Other Comprehensive Income (Loss), Net of Tax	Other Comprehensive Income (Loss), Net of Tax
Included in earnings attributable to realized gains / losses	$ 0	$ 24	$ 0	$ (148)
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Realized Investment Gains (Losses)	Realized Investment Gains (Losses)	Realized Investment Gains (Losses)	Realized Investment Gains (Losses)
Amortization of bond premium and discount, net	$ 0	$ 1	$ 0	$ 5
Purchases	0	182	0	295
Sales	0	(428)	0	(1,164)
Ending balance	0	3,569	0	3,569
Gains (losses) included in earnings attributable to the change in unrealized gains (losses) related to assets still held at end of reporting period	$ 0	$ 31	$ 0	$ (131)
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax	OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax	OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax	OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax

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