Equity and Redeemable Non-controlling Interest - Schedule of Company's Outstanding Shares of Common Stock (Parenthetical) (Detail) - Class I Shares [Member] $ in Millions	9 Months Ended
Sep. 30, 2018 USD ($)
Class of Stock [Line Items]
Independent directors' restricted stock grant, value	$ 0.1
Amoritzation period of grant	1 year

Aggregate value of stock related to Restricted Stock Awards issued during the period.

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-Name Accounting Standards Codification
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-Section S99
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-Name Accounting Standards Codification
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Name:	us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration