Treasury Stock Acquisition (Parenthetical) (Detail)	9 Months Ended
Sep. 30, 2018 shares
Long Term Incentive Plan
Schedule of Treasury Stock [Line Items]
Employees’ tax withholding obligations upon vesting of restricted shares	561,807

The number of restricted shares issued as compensation, net of shares for the payment of withholding taxes. This element is to be used only if shares are used in lieu of cash to satisfy all or a portion of withholding taxes.

No definition available.

Name:	us-gaap_RestrictedStockSharesIssuedNetOfSharesForTaxWithholdings
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration