Supplemental Disclosure to Statements of Cash Flows (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Supplemental Disclosure [Line Items]
Write-off of fully depreciated property and deferred costs	$ 127,005	$ 48,373	$ 76,714
Assumption of mortgage loans	0	2,833	0
Equity contribution from unconsolidated joint venture partner	3,500	0	0
Proceeds from Issuance of Preferred Limited Partners Units	$ 16,597	$ 0	$ 0