Summary of Significant Accounting Policies - Revenue Recognition (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Mar. 27, 2017	Feb. 09, 2017
Revenue Recognition
Estimated amount of real estate taxes, which are the responsibility of tenants	$ 3,000,000	$ 2,600,000	$ 6,200,000	$ 5,200,000
Net income (loss)	1,368,000	(9,941,000)	1,437,000	2,391,000
State and local income, excise and franchise taxes	200,000	$ 300,000	400,000	$ 500,000
Buena Vista, VA, Q3 2012 [Member]
Revenue Recognition
Lease termination fee receivable					$ 500,000
Buena Vista, VA, Q3 2012 [Member] | Rental income
Revenue Recognition
Gain (Loss) on Contract Termination	100,000		200,000
Belvidere, IL, Q2 2013, Six [Member]
Revenue Recognition
Lease termination fee receivable						$ 54,000
Belvidere, IL, Q2 2013, Six [Member] | Rental income
Revenue Recognition
Gain (Loss) on Contract Termination			54,000
Golden, CO, Q1 2013 [Member] | Rental income
Revenue Recognition
Gain (Loss) on Contract Termination	$ 200,000		$ 400,000