Real Estate Properties - Narrative (Details) $ in Thousands	1 Months Ended	6 Months Ended		12 Months Ended
	Jan. 31, 2013 building	Jun. 30, 2016 USD ($) ft² building	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($) ft² land_parcel building property
Real Estate Properties [Line Items]
Real estate improvements | $		$ 59,200	$ 27,800
Number of properties held for sale | property				0
Number of buildings sold | building	18
Disposed of by Sale
Real Estate Properties [Line Items]
Number of properties sold | property				91
Number of buildings sold | building		31		135
Number of land parcels | land_parcel				1
Square Footage (in sqft) | ft²		2,039,997		18,900,000
Gross sales price | $		$ 413,765		$ 2,000,000