Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands		3 Months Ended		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Assets
Impairment charge		$ 4,100		$ 4,132		$ 0		$ 1,417
Nonrecurring | Buildings and Improvements
Assets
Buildings and improvements, net		19,000	[1]	19,000	[1]	25,000	[2]
Impairment charge				4,100	[1]	1,400	[2]
Nonrecurring | Buildings and Improvements | Discounted cash flow
Assets
Buildings and improvements, net		19,000	[3]	19,000	[3]	25,000	[4]
Nonrecurring | Level 3 | Buildings and Improvements
Assets
Buildings and improvements, net		19,000	[1]	$ 19,000	[1]	25,000	[2]
Nonrecurring | Level 3 | Buildings and Improvements | Discounted cash flow
Assets
Discount rate	[5]			8.00%
Terminal capitalization rate	[5]			7.00%
Nonrecurring | Level 1 | Buildings and Improvements
Assets
Buildings and improvements, net		0	[1]	$ 0	[1]	0	[2]
Nonrecurring | Level 2 | Buildings and Improvements
Assets
Buildings and improvements, net		$ 0	[1]	$ 0	[1]	$ 0	[2]
Nonrecurring | Minimum | Buildings and Improvements
Assets
Discount rate	[4]					7.50%
Nonrecurring | Minimum | Buildings and Improvements | Discounted cash flow
Assets
Terminal capitalization rate	[4]					6.50%
Nonrecurring | Maximum | Buildings and Improvements
Assets
Discount rate	[4]					8.00%
Nonrecurring | Maximum | Buildings and Improvements | Discounted cash flow
Assets
Terminal capitalization rate	[4]					7.50%

[1] We recorded non-cash impairment charge of $4.1 million during the year ended December 31, 2017 as a result of a measurable decrease in the fair value of 22 Exchange.

[2] We recorded a non-cash impairment charge of $1.4 million during the year ended December 31, 2015 as a result of a measurable decrease in the fair value of 22 Exchange, one of our student housing investments.

[3] We recorded a non-cash impairment charge of $4.1 million during the year ended December 31, 2017 on our investment in 22 Exchange, one of our student housing investments.

[4] Due to the local market decline in Akron, Ohio, we recorded a non-cash impairment charge of $1.4 million on our investment in 22 Exchange, a student housing property, during the year ended December 31, 2015.

[5] We recorded a non-cash impairment charge of $4.1 million on our investment in 22 Exchange during the year ended December 31, 2017.