Business Acquisitions (Details Textual) - Property, Plant and Equipment, Type [Domain] - Scenario, Unspecified [Domain] - Subsequent Event Type [Domain] $ in Thousands, shares in Millions, CAD in Millions	1 Months Ended			2 Months Ended	3 Months Ended		12 Months Ended
	Jan. 30, 2015 USD ($) shares	Jan. 31, 2014 USD ($)	Jul. 31, 2013 CAD	Mar. 31, 2015 USD ($) shares	Mar. 31, 2015 USD ($) shares	Mar. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Jun. 25, 2015	Dec. 31, 2014 USD ($)	Feb. 26, 2013 USD ($)
Payments to Acquire Businesses, Gross					$ 7,700
Income (Loss) from Equity Method Investments					(2,149)	$ 319
Business Combination, Step Acquisition, Equity Interest in Acquiree, Remeasurement Loss							$ 300
Business Combination, Separately Recognized Transactions, Revenues and Gains Recognized						700
Business Combination, Separately Recognized Transactions, Expenses and Losses Recognized					1,300	300
Business Combination, Separately Recognized Transactions, Net Gains and Losses					33,400
Limited Partnership Units Of Operating Partnership Units Issued | shares	10.4
Other Liabilities				$ 47,071	$ 47,071				$ 22,092
Amortization	$ 1,000
Cb Portfolio Acquisition [Member]
Our Ownership										48.00%
Equity Method Investment, Ownership Percentage										48.00%
Cb Portfolio Acquisition [Member] | Purchase and Sale Agreement [Member]
Our Ownership										48.00%
Equity Method Investment, Ownership Percentage										48.00%
Copper Beech [Member]
Business Acquisitions Costs Of Acquired Entity Purchase Price										$ 230,600
Our Ownership				100.00%	100.00%		67.00%		48.00%
Income (Loss) from Equity Method Investments					$ 21,600
Business Combination, Contingent Consideration Arrangements, Description					100% interest in 25 student housing properties; 100% interest in 2 undeveloped land parcels and 1 corporate office building; 85% interest in 1 student housing property (Copper Beech Klondike or CBTC 8); 84% interest in 1 student housing property (Copper Beech Northbrook or CBTC 9); 48% interest in 7 student housing properties; and no ownership interest in 1 student housing property (Copper Beech Kalamazoo Phase I).
Business Combination, Separately Recognized Transactions, Expenses and Losses Recognized					$ 1,300	500
Business Combination, Separately Recognized Transactions, Net Gains and Losses					$ 21,600
Equity Method Investment, Ownership Percentage				100.00%	100.00%		67.00%		48.00%
Other Liabilities				$ 6,300	$ 6,300
Amortization					$ 13,000	$ 13,000
DCV Holdings, LP [Member]
Payments to Acquire Interest in Joint Venture | CAD			CAD 60.0
CSH Montreal LP [Member]
Our Ownership				47.00%	47.00%				47.00%
Equity Method Investment, Ownership Percentage				47.00%	47.00%				47.00%
First CB Closing [Member]
Business Combination, Acquisition Related Costs					$ 58,900
Business Combination, Separately Recognized Transactions, Revenues and Gains Recognized					9,200
Business Combination, Separately Recognized Transactions, Net Gains and Losses					$ 7,300
Limited Partnership Units Of Operating Partnership Units Issued | shares				10.4	10.4
Limited Partnership Units Of Operating Partnership Units Issued Value				$ 71,300	$ 71,300
Depreciation				2,800
Amortization				$ 8,700
Second CB Closing [Member]
Business Combination, Acquisition Related Costs					$ 1,400
Limited Partnership Units Of Operating Partnership Units Issued | shares				2.0	2.0
Limited Partnership Units Of Operating Partnership Units Issued Value				$ 13,000	$ 13,000
Copper Beech Kalamazoo [Member]
Our Ownership				48.00%	48.00%
Equity Method Investment, Ownership Percentage				48.00%	48.00%
Copper Beech Klondike And Copper Beech Northbrook [Member]
Our Ownership								100.00%
Equity Method Investment, Ownership Percentage								100.00%
Harrison Street Real Estate [Member]
Our Ownership		80.00%
Equity Method Investment, Ownership Percentage		80.00%
Harrison Street Real Estate Campus Crest [Member]
Business Combination, Step Acquisition, Equity Interest in Acquiree, Fair Value		$ 1,900
Grove At Stateboro Georgia [Member]
Our Ownership		20.00%
Equity Method Investment, Ownership Percentage		20.00%
The Grove at Denton, Texas [Member]
Payments to Acquire Businesses, Gross					$ 7,700