Property Acquisitions (Details Textual) (USD $) Share data in Millions, unless otherwise specified	3 Months Ended			1 Months Ended	3 Months Ended	12 Months Ended						3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Feb. 28, 2013 Cb Portfolio Acquisition [Member]	Mar. 31, 2013 Cb Portfolio Acquisition [Member]	Dec. 31, 2012 Cb Portfolio Acquisition [Member]	Mar. 31, 2013 Cb Portfolio Acquisition [Member] Cb Investors [Member]	Feb. 28, 2013 Cb Portfolio Acquisition [Member] Cb Investors [Member]	Feb. 28, 2013 Cb Portfolio Acquisition [Member] Members Of Cbtc and Cbtc Pa [Member]	Feb. 28, 2013 Cb Portfolio Acquisition [Member] Non Member Investors [Member]	Feb. 28, 2013 Cb Portfolio Acquisition [Member] Purchase and Sale Agreement [Member]	Mar. 31, 2013 Copper Beech [Member]	Feb. 28, 2013 Copper Beech [Member]	Mar. 31, 2013 Six Properties Cb Portfolio Acquisition [Member]	Feb. 26, 2013 Copper Beech Townhome Communities [Member]	Mar. 31, 2013 Campus Crest At Toledo Ohio [Member]
Business Acquisition, Cost of Acquired Entity, Purchase Price	$ 13,801,000				$ 230,200,000								$ 230,200,000	$ 121,400,000		$ 13,800,000
Company Ownership Percentage				48.00%				52.00%	36.30%	11.70%	48.00%				48.00%
Business Acquisition, Cost of Acquired Entity, Liabilities Incurred											106,700,000			74,300,000
Description On Steps In Portfolio Acquisition				On March 18, 2013, we acquired a 48.0% interest in six properties that did not require lender consent prior to sale and on April 15, 2013, we acquired a 48% interest in an additional property. We will close on our 48.0% interest in each remaining property at such time as we obtain the requisite lender consent relating thereto. We expect to obtain all such consents and close on our 48.0% interest in all properties comprising the CB Portfolio by the end of the third quarter of 2013.
Student Housing Properties Average Age In Year					7 years
Average Occupancy Percentage Of Student Housing Properties					98.50%
Business Acquisition, Cost of Acquired Entity, Cash Paid					13,000,000
Due from Other Related Parties							31,700,000
Investment in unconsolidated entities	165,688,000		22,555,000											47,100,000
Income (Loss) from Equity Method Investments	410,000	(60,000)			300,000
Investment Income, Interest					100,000
Business Combination, Acquisition Related Costs					300,000							9,400,000
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares					25.5
Average Monthly Total Revenue Per Occupied Bed						$ 470
Mortgage Loans on Real Estate, Interest Rate	8.50%
Mortgage Loans On Real Estate Interest Rate Of Tem Period	3 years