Real Estate Notes Receivable (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2013 promissory_notes	Dec. 31, 2012
Portfolio One
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of promissory notes secured by office buildings	4
Total real estate notes receivable	$ 20.0	$ 20.0
Interest rate, minimum	10.85%
Interest rate, maximum	10.95%
Interest rate	14.57%
Portfolio Two
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of promissory notes secured by office buildings	2
Total real estate notes receivable	$ 8.5
Interest rate	7.00%