Real Estate Properties - Narrative (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2017 USD ($) ft² building	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($) ft² building property
Real Estate Properties [Line Items]
Real estate improvements | $	$ 14,200	$ 31,900
Number of properties held for sale | property			0
Disposed of by Sale
Real Estate Properties [Line Items]
Number of properties sold | property			30
Number of buildings sold | building	3		62
Square footage (in sqft) | ft²	827,204		8,000,000
Gross sales price | $	$ 113,125		$ 1,300,000