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Note Receivables - Additional Information (Detail) - USD ($) $ in Thousands |  | 3 Months Ended | 9 Months Ended
--- | --- | --- | ---
Dec. 29, 2017 | Sep. 30, 2018 | Sep. 30, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Interest rate | 5.00% | 5.00% | 5.00%
Percentage of interest rate increase at the event of default | 10.00% | 10.00% | 10.00%
Promissory note maturity date |  |  | Dec. 29, 2021
Interest income recognized |  | $ 533 | $ 1,373
AdvisorEngine [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Aggregate commitment amount | $ 30,000 |  |
AdvisorEngine [Member] | Equity Option [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Aggregate commitment amount | 30,000 |  |
Fair value of option | $ 3,278 | $ 3,278 | $ 3,278

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