Annual report pursuant to Section 13 and 15(d)

Related-Party Transactions - Additional Information (Detail)

v3.20.4
Related-Party Transactions - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Related Party Transaction [Line Items]      
Operating lease cost $ 25,508,000 $ 24,372,000  
Aggregate principal amount for employee notes receivable 431,000 388,000  
MMC [Member]      
Related Party Transaction [Line Items]      
Real estate brokerage commissions and financing fees from transactions with subsidiaries of Marcus & Millichap Company 2,900,000 5,200,000 $ 7,700,000
Commission expenses for transactions with subsidiaries of Marcus & Millichap Company 1,700,000 3,000,000.0 4,600,000
Operating lease cost $ 1,300,000 1,300,000 1,000,000.0
Lease expiration date May 31, 2022    
Accounts payable and other liabilities - related party $ 89,000 88,000  
MMC [Member] | Transition Services Agreement [Member]      
Related Party Transaction [Line Items]      
Selling, general and administrative expense $ 68,000 $ 127,000 $ 197,000
George M. Marcus [Member]      
Related Party Transaction [Line Items]      
Beneficial ownership percentage 40.00%