Investments in Real Estate and Real Estate Under Construction - Summary of forward purchase commitments (Details) ft² in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) ft²	Mar. 31, 2017 ft²
Real Estate [Line Items]
Square Feet (000's) | ft²	475	366
Maximum Acquisition Cost	$ 71,725
Industrial Property [Member] | Grand Prairie, TX [Member]
Real Estate [Line Items]
Square Feet (000's) | ft²	215
Maximum Acquisition Cost	$ 24,725
Approximate Lease Term (Yrs)	20 years
Industrial Property [Member] | Warren, MI [Member]
Real Estate [Line Items]
Square Feet (000's) | ft²	260
Maximum Acquisition Cost	$ 47,000
Approximate Lease Term (Yrs)	15 years
Letters of credit outstanding, amount	$ 4,600