Investments in Unconsolidated Joint Ventures - Related Party (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Cambridge Medipark Ltd [Member]
Related Party Transaction [Line Items]
Notes Payable, Related Parties	$ 3,000,000	$ 3,000,000
United Kingdom [Member] | Kings Hill Unit Trust [Member]
Related Party Transaction [Line Items]
Accounts Receivable, Related Parties	109,000	137,000
Notes Receivable, Related Parties	14,400,000	13,300,000
Related Party Transaction Rate Range, Min	2.00%
Related Party Transaction Rate Range, Max	10.00%
Related Party Transaction, Due Date	1/1/2017
Prepaid Expense, Related Party	46,000	56,000
United Kingdom [Member] | Blythe Valley JV Sarl [Member]
Related Party Transaction [Line Items]
Accounts Receivable, Related Parties	127,000	151,000
United Kingdom [Member] | Cambridge Medipark Ltd [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due Date	0
Related Party Transaction, Rate	0.00%
Metro [Member] | Liberty Washington, LP [Member]
Related Party Transaction [Line Items]
Due to Related Parties	0	223,000
Due from Related Parties	1,200,000	1,200,000
Metro [Member] | Liberty Commerz 1701 JFK Boulevard, LP [Member]
Related Party Transaction [Line Items]
Due from Related Parties	266,000	2,200,000
Accounts Receivable, Related Parties	$ 175,000	$ 272,000