Effect of Derivative Financial Instruments on Consolidated Statements of Income and Comprehensive Income (Detail) (Derivatives in Cash Flow Hedging Relationships, Interest Rate Swap, USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Derivative [Line Items]
Amount of loss recognized in OCI on derivative (effective portion)	$ 471	$ 336	$ 1,271	$ 336
Interest Expense
Derivative [Line Items]
Amount of loss reclassified from accumulated OCI into income (effective portion)	$ 437		$ 859