Investments in Unconsolidated Joint Ventures - Related Party (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Cambridge Medipark Ltd [Member]
Related Party Transaction [Line Items]
Notes Payable, Related Parties	$ 3,100,000
United Kingdom [Member] | Kings Hill Unit Trust [Member]
Related Party Transaction [Line Items]
Accounts Receivable, Related Parties	137,000	147,000
Notes Receivable, Related Parties	10,800,000	4,300,000
Related Party Transaction, Date	1/1/2017
Related Party Transaction Rate Range, Min	2.00%
Related Party Transaction Rate Range, Max	10.00%
United Kingdom [Member] | Blythe Valley JV Sarl [Member]
Related Party Transaction [Line Items]
Accounts Receivable, Related Parties	151,000	101,000
Notes Receivable, Related Parties	12,400,000	8,500,000
Related Party Transaction, Date	12/1/2017
Related Party Transaction Rate Range, Min	2.00%
Related Party Transaction Rate Range, Max	10.00%
United Kingdom [Member] | Cambridge Medipark Ltd [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Description of Transaction	0
Related Party Transaction, Rate	0.00%
Metro [Member] | Liberty Washington, LP [Member]
Related Party Transaction [Line Items]
Due to Related Parties	223,000	236,000
Due from Related Parties	1,200,000	2,000,000
Metro [Member] | Liberty/Commerz 1701 JFK Boulevard, LP [Member]
Related Party Transaction [Line Items]
Due from Related Parties	2,200,000	2,600,000
Accounts Receivable, Related Parties	$ 272,000	$ 420,000