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Note Receivables - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Sep. 30, 2018	Jun. 30, 2018	Dec. 29, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest rate	5.00%
Percentage of interest rate increase at the event of default	10.00%
Promissory note maturity date	Dec. 29, 2021
AdvisorEngine [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Aggregate commitment amount				$ 30,000
Current funding amount				22,000
Remaining commitment amount	$ 8,000
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
AdvisorEngine [Member] | Scenario, Forecast [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Remaining commitment amount		$ 3,000	$ 5,000

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Fair value portion of investments accounted under the cost method.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 325
-SubTopic 20
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=75030709&loc=d3e39828-111592

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Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Debt instrument, interest rate, increase (decrease) on event of default.

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Notes and loans receivable aggregate commitment amount.

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- Definition

Notes and loans receivable current funding amount.

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Notes and loans receivable remaining commitment amount.

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