Significant Accounting Policies Revenues - Accounts Receivables (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other Receivables	$ 10,166	$ 8,476
Allowance for Doubtful Accounts Receivable	(3,442)	(4,819)
Accounts Receivable, Net	37,733	36,600
CAM and Tax Reimbursements [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross	26,355	13,629
Tenant Receivables [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross	$ 4,654	$ 19,314