Investments in Real Estate - Investments in Existing Properties (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Real Estate Investments, Net [Abstract]
Capitalized costs on existing properties	$ 12,300	$ 9,500
Re-leasing costs	2,800	1,200
Recurring capital expenditures	529	536
Nonrecurring building improvements	$ 8,900	$ 7,800