Real Estate Properties - Summary of Properties Held for Sale (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($) ft² building property	Dec. 31, 2016 property
Real Estate Properties [Line Items]
Number of Properties		0
Held-for-sale
Real Estate Properties [Line Items]
Number of Properties	2
Number of Buildings | building	5
Square Footage (in sqft) | ft²	630,326
Gross Sales Price | $	$ 64,500
Held-for-sale | 25 S. Charles Street
Real Estate Properties [Line Items]
Number of Properties	1
Number of Buildings | building	1
Square Footage (in sqft) | ft²	359,254
Gross Sales Price | $	$ 24,500
Held-for-sale | Parkshore Plaza
Real Estate Properties [Line Items]
Number of Properties	1
Number of Buildings | building	4
Square Footage (in sqft) | ft²	271,072
Gross Sales Price | $	$ 40,000