Schedule of Interest Rate Swap Agreements on Accumulated Other Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Ending balance	$ (245,239)	$ (212,123)
Interest Rate Swap
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Beginning balance	(218,451)	(47,676)
Unrealized loss on interest rate swaps	(139,474)	(273,389)
Reclassification of net losses included in income statement	85,842	102,614
Ending balance	$ (272,083)	$ (218,451)