Supplemental Disclosure to Statements of Cash Flows (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011
Supplemental Disclosure to Statements of Cash Flows [Abstract]
Write-off of fully depreciated property and deferred costs	$ 12,783	$ 9,595
Write Off Of Depreciated Property And Deferred Costs Due To Sale	94,762	90,087
Discount on preferred unit redemption net of origination costs	$ 2,811	$ 0