Fair Value of Interest Rate Derivative Contracts Designated as Hedging Instruments (Detail) (Designated as Hedging Instrument, Interest rate derivative contracts, Accounts Payable, USD $) In Thousands, unless otherwise specified	Dec. 31, 2011
Designated as Hedging Instrument | Interest rate derivative contracts | Accounts Payable
Derivatives, Fair Value [Line Items]
Fair value of interest rate derivative contracts	$ 25,927