Earnings Per Share - Schedule of Computations of Weighted Average Shares Outstanding (Parenthetical) (Detail) - shares shares in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2018
Share Based Awards [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Potentially dilutive restricted share awards excluded from computation of diluted EPS	0.8	0.9

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.

Name:	us-gaap_EarningsPerShareDilutedLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration