Derivatives Interest Rate Swap Agreements - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2012	Mar. 31, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Derivative [Line Items]
Effective hedge losses reclassified into earnings	$ 51,883		$ 150,557	$ 85,842	$ 260,244
Ineffective losses recorded on a current basis in earnings	17		(130)	(321)	(515)
Estimated amount related to derivatives reclassified to interest expense during the next 12 months				120,235
Future cash flows for forecasted transactions, average period in months				34 months
Maximum leverage ratio the Company can reach before it could be in default of one of its derivative obligations		10 to 1
Fair value of derivatives in net liability position, which includes accrued interest but excludes any adjustment for nonperformance risk, related to agreements	$ 273,120			$ 273,120