Impairment Charges, Impairment of Joint Venture Investments and Reserves - Summary of Significant Unobservable Inputs (Parenthetical) (Detail)	12 Months Ended
Dec. 31, 2017
Weighted Average [Member]
Schedule Of Investments [Line Items]
Terminal capitalization rate, Weighted-average rate	8.80%

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.

No definition available.

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration