Supplemental Disclosure to Statements of Cash Flows (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Supplemental Disclosure to Statements of Cash Flows [Abstract]
Write off of fully depreciated property and deferred costs	$ 17,784	$ 12,783
Write off of depreciated property and deferred costs due to sale	49,618	94,762
Write off of origination costs relating to preferred unit redemptions	$ 1,236	$ 2,811