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Description of Business, Basis of Presentation and Recent Accounting Pronouncements - Additional Information (Detail) | 3 Months Ended
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Mar. 31, 2021 USD ($) Office | Mar. 31, 2020 Office
Class of Stock [Line Items] |  |
Number of offices | Office | 84 |
Formation date | 2013-06 |
Percentage of common stock distributed | 80.00% |
Commission's receivable settled period | 10 days |
Line of credit | $ | $ 0 |
Credit Agreement [Member] |  |
Class of Stock [Line Items] |  |
Line of credit | $ | $ 0 |
Transaction Risk [Member] |  |
Class of Stock [Line Items] |  |
Concentration risk percentage | 0.00% | 0.00%
Customer Concentration Risk [Member] | Total revenues [Member] |  |
Class of Stock [Line Items] |  |
Concentration risk percentage | 10.00% | 10.00%
Customer Concentration Risk [Member] | Commissions receivable [Member] |  |
Class of Stock [Line Items] |  |
Concentration risk percentage | 10.00% | 10.00%
Geographic Concentration Risk [Member] | Total revenues [Member] |  |
Class of Stock [Line Items] |  |
Number of offices | Office | 0 | 1
Concentration risk percentage | 10.00% | 10.00%
Geographic Concentration Risk [Member] | Total revenues [Member] | Maximum [Member] | CANADA [Member] |  |
Class of Stock [Line Items] |  |
Concentration risk percentage | 2.00% | 2.00%
IPO MMI [Member] |  |
Class of Stock [Line Items] |  |
IPO completion date | Nov. 05, 2013 |

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