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Related-Party Transactions - Additional Information (Detail) - USD ($) | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2021 | Jun. 30, 2020 | Jun. 30, 2021 | Jun. 30, 2020 | Dec. 31, 2020
Related Party Transaction [Line Items] |  |  |  |  |
Operating lease cost | $ 6,512,000 | $ 6,341,000 | $ 13,101,000 | $ 12,604,000 |
Aggregate principal amount for employee notes receivable | 125,000 |  | 125,000 |  | $ 431,000
MMC [Member] |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |
Real estate brokerage commissions and financing fees from transactions with subsidiaries of Marcus & Millichap Company | 337,000 | 880,000 | 794,000 | 1,600,000 |
Commission expenses for transactions with subsidiaries of Marcus & Millichap Company | 203,000 | 536,000 | 477,000 | 988,000 |
Operating lease cost | 332,000 | 332,000 | $ 665,000 | 665,000 |
Lease expiration date |  |  | May 31, 2022 |  |
Accounts payable and other liabilities - related party | 85,000 |  | $ 85,000 |  | $ 89,000
MMC [Member] | Transition Services Agreement [Member] | Selling, General and Administrative Expenses [Member] |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |
Selling, general and administrative expense | $ (4,000) | $ 16,000 | $ 15,000 | $ 42,000 |
George M. Marcus [Member] |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |
Beneficial ownership percentage |  |  | 38.00% |  |

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