Effects of Changes in Fair Values of Derivatives Designated As Cash Flow Hedges on Accompanying Consolidated Statements of Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Derivative Instruments, Gain (Loss) [Line Items]
Loss recognized in OCI (effective portion)	$ 0	$ 0	$ (882)
Interest Rate Swap | Cash Flow Hedging | Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Loss reclassified from AOCI (effective portion)	$ (6,314)	$ (11,657)	$ (19,619)