Earnings per Share - Additional Information (Detail) - shares	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings per share [line items]
Antidilutive securities	0		0
Series L share [member]
Earnings per share [line items]
Effect of dilutive potential shares	27,910,000	27,910,000

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

No definition available.

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