Concentrations of Credit Risk - Additional Information (Detail) $ in Millions	Dec. 31, 2017 USD ($)
Risks And Uncertainties [Abstract]
Cash, cash equivalents, and restricted cash	$ 115.5

This item represents disclosure of all significant concentrations of credit risk or market risk arising from the subject financial instrument (as defined), whether from an individual counterparty or groups of counterparties.

No definition available.

Name:	us-gaap_FairValueConcentrationOfRiskCashAndCashEquivalents
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant