Interes Rates on Senior Secured Credit Facilities (Parenthetical) (Detail)	6 Months Ended
Jun. 30, 2018
Debt Instrument [Line Items]
Unused commitment fee	0.30%
Letter of credit fee	1.75%

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