Quarterly report pursuant to Section 13 or 15(d)

Notes Receivable from Partners - Additional Information (Detail)

v3.21.2
Notes Receivable from Partners - Additional Information (Detail) - Partners - USD ($)
9 Months Ended
Sep. 30, 2021
Dec. 31, 2020
Dec. 31, 2019
Related Party Transaction [Line Items]      
Term of promissory notes receivable in the form of five or six year interest-bearing promissory notes and/or in the form of nine year interest-bearing limited recourse promissory notes    
Notes receivable from partners $ 604,000 $ 353,000 $ 645,000
Allowance for credit losses on notes receivable 0 0  
Full Recourse      
Related Party Transaction [Line Items]      
Notes receivable from partners 604,000 353,000  
Limited Recourse      
Related Party Transaction [Line Items]      
Notes receivable from partners $ 0 $ 0