Management's Plans Regarding Liquidity and Capital Resources - Additional Information (Detail) - Affiliated Entity [Member] - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Liquidity And Managements Plans [Line Items]
Percentage of fund owed by Shareholders	100.00%
Loans outstanding to affiliated companies	$ 14.7	$ 11.9

Amount of principal loans outstanding to affiliates for management investment companies.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 320
-Section S99
-Paragraph 6
-Subparagraph (SX 210.12-14.Column B)
-URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611322-123010

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant