Real Estate Assets - Additional Information (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) ft²
Merrillville, IN
Real Estate Properties [Line Items]
Leasable square feet of traditional drive-up storage units and all-climate-controlled units	13,300
Aggregate cost to expansion of storage facilities | $	$ 400,000
Millbrook, NY
Real Estate Properties [Line Items]
Leasable square feet of traditional drive-up storage units and all-climate-controlled units	16,500
Estimate for expansion relating to construction cost	The planning for the Millbrook, NY expansion is under development and the Company is actively evaluating proposals for its construction. As of December 31, 2017, a final estimate of construction costs has not yet been determined.