Commitments and Contingencies - Additional Information (Detail) - USD ($)	Sep. 30, 2021	Dec. 31, 2020
Other Commitments [Line Items]
Outstanding loan commitments	$ 384,900,000	$ 126,000,000.0
Future commitments outstanding related to investments	9,100,000
Performance Stand-by Letters of Credit [Member]
Other Commitments [Line Items]
Outstanding stand-by letters of credit	655,000	0
Financial Stand-by Letters of Credit [Member]
Other Commitments [Line Items]
Outstanding stand-by letters of credit	3,600,000	6,100,000
Other Liabilities [Member]
Other Commitments [Line Items]
Reserves for unfunded commitments to borrowers	$ 512,000	$ 0