Investments in Real Estate - Investments in Existing Properties (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Investments in Real Estate
Capitalized costs on existing properties	$ 3,200,000	$ 3,400,000
Re-leasing costs	917,000	410,000
Recurring capital expenditures	11,000	341,000
Nonrecurring building improvements	$ 2,300,000	$ 2,600,000