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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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- 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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Fair value portion of investments accounted under the cost method.

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- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-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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- Definition

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/disclosureRef
-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

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
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Notes and loans receivable aggregate commitment amount.

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Paid-in-kind interest income.

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