Regulatory Capital and Liquidity Requirements - Summary of Applicable Capital and Liquidity Amounts and Requirements by Agencies (Detail) $ in Thousands		Sep. 30, 2024 USD ($)	Dec. 31, 2023 USD ($)
Capital Requirements By Agencies [Line Items]
Net worth, Actual	[1]	$ 865,895	$ 874,628
Net worth, Required	[1]	$ 580,944	$ 584,131
Tangible net worth / total assets ratio, Actual	[1]	0.13	0.15
Tangible net worth / total assets ratio, Required	[1]	0.06	0.06
Liquidity, Actual	[1]	$ 587,218	$ 450,210
Liquidity, Required	[1]	$ 219,026	$ 210,691

[1] Calculated in accordance with the Agencies’ requirements.