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Related-Party Transactions - Additional Information (Detail) - USD ($) | 3 Months Ended |
--- | --- | ---
Mar. 31, 2021 | Mar. 31, 2020 | Dec. 31, 2020
Related Party Transaction [Line Items] |  |  |
Operating lease cost | $ 6,589,000 | $ 6,263,000 |
Aggregate principal amount for employee notes receivable | 178,000 |  | $ 431,000
MMC [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Real estate brokerage commissions and financing fees from transactions with subsidiaries of Marcus & Millichap Company | 457,000 | 766,000 |
Commission expenses for transactions with subsidiaries of Marcus & Millichap Company | 274,000 | 453,000 |
Operating lease cost | $ 333,000 | 333,000 |
Lease expiration date | May 31, 2022 |  |
Accounts payable and other liabilities - related party | $ 93,000 |  | $ 89,000
MMC [Member] | Transition Services Agreement [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Selling, general and administrative expense | $ 19,000 | $ 26,000 |
George M. Marcus [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Beneficial ownership percentage | 39.00% |  |

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