Nonvested Restricted Shares Activity (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Nonvested shares, intrinsic value	$ 0.2	$ 0.1

Intrinsic value of equity-based compensation awards not vested. Excludes stock and unit options.

No definition available.

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