Supplemental Cash Flow Information (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Supplemental Cash Flow Information [Abstract]
Interest paid	$ 404,443	$ 409,293	$ 331,681
Income taxes paid (refund)	4,340	(5,935)	5,597
Increase (decrease) in the fair value of forward-starting interest rate swaps (note 7)	0	(114,157)	(140,397)
Assets acquired through capital leases and installment sales	$ 27,094	$ 18,682	$ 17,351