Interest Paid (Parenthetical) (Detail) $ in Millions	9 Months Ended
Sep. 30, 2017 USD ($)
Series 2007-1 Notes [Member]
Debt Instrument [Line Items]
Prepayment penalities of Notes	$ 7.0

The cash outflow for incremental, external costs directly pertaining to an early extinguishment of debt, including legal costs and prepayment penalties, and excluding interest and repayment of debt principal.

No definition available.

Name:	us-gaap_PaymentsOfDebtExtinguishmentCosts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration