Summary of Significant Accounting Policies - Revenues - Accounts Receivables (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for doubtful accounts	$ 3,000	$ 3,200	$ 4,000
Other receivables	8,582	10,166
Less: allowance for doubtful accounts	(3,915)	(3,442)
Accounts Receivable, Net	26,601	37,733
CAM and Tax Reimbursements
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross	17,891	26,355
Tenant Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross	4,043	4,654
Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage Of Revenue By Customer	5.00%
Discontinued Operations [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for doubtful accounts	$ 0	$ 151	$ 56