Senior Debt - Summary of Debt (Parenthetical) (Detail)	6 Months Ended
Jun. 30, 2018
Term Loan [Member]
Debt Instrument [Line Items]
Term loans, year of maturity	2020-09

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