Effect of Derivative Financial Instruments on Consolidated Statements of Income and Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Derivative [Line Items]
Amount of loss recognized in OCI on derivative (effective portion)	$ 494	$ 3,020	$ 1,765	$ 3,356
Derivatives in Cash Flow Hedging Relationships | Interest Expense | Interest Rate Swap
Derivative [Line Items]
Amount of loss reclassified from accumulated OCI into income (effective portion)	$ 440	$ 463	$ 1,299	$ 463