Recent Acquisitions of Real Estate (Revenue and Net Income) (Details) - Two Years Prior Acquisitions $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Rookwood
Business Acquisition, Pro Forma Information
Revenue of acquiree	$ 19,507
Net income (loss) of acquiree	(7,041)
Montrose Student Residences
Business Acquisition, Pro Forma Information
Revenue of acquiree	2,579
Net income (loss) of acquiree	(3,049)
Queens Court
Business Acquisition, Pro Forma Information
Revenue of acquiree	1,200
Net income (loss) of acquiree	$ (1,415)