Real Estate (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) ft² a bldg
Building and Building Improvements
Property, Plant and Equipment [Line Items]
Number of buildings (in buildings) | bldg	5
Leaseable Square Feet (in sqft) | ft²	1,069,670
Acres of Developable Land
Property, Plant and Equipment [Line Items]
Acres of Developable Land (in acres) | a	179.7
Land, Buildings and Improvements
Property, Plant and Equipment [Line Items]
Purchase Price (in thousands) | $	$ 135,118
Dallas | Building and Building Improvements
Property, Plant and Equipment [Line Items]
Number of buildings (in buildings) | bldg	2
Leaseable Square Feet (in sqft) | ft²	509,733
Dallas | Acres of Developable Land
Property, Plant and Equipment [Line Items]
Acres of Developable Land (in acres) | a	0.0
Dallas | Land, Buildings and Improvements
Property, Plant and Equipment [Line Items]
Purchase Price (in thousands) | $	$ 44,400
Southern California | Building and Building Improvements
Property, Plant and Equipment [Line Items]
Number of buildings (in buildings) | bldg	1
Leaseable Square Feet (in sqft) | ft²	289,683
Southern California | Acres of Developable Land
Property, Plant and Equipment [Line Items]
Acres of Developable Land (in acres) | a	0.0
Southern California | Land, Buildings and Improvements
Property, Plant and Equipment [Line Items]
Purchase Price (in thousands) | $	$ 31,285
United Kingdom | Building and Building Improvements
Property, Plant and Equipment [Line Items]
Number of buildings (in buildings) | bldg	0
Leaseable Square Feet (in sqft) | ft²	0
United Kingdom | Acres of Developable Land
Property, Plant and Equipment [Line Items]
Acres of Developable Land (in acres) | a	25.0
United Kingdom | Land, Buildings and Improvements
Property, Plant and Equipment [Line Items]
Purchase Price (in thousands) | $	$ 2,658
Atlanta | Building and Building Improvements
Property, Plant and Equipment [Line Items]
Number of buildings (in buildings) | bldg	0
Leaseable Square Feet (in sqft) | ft²	0
Atlanta | Acres of Developable Land
Property, Plant and Equipment [Line Items]
Acres of Developable Land (in acres) | a	154.7
Atlanta | Land, Buildings and Improvements
Property, Plant and Equipment [Line Items]
Purchase Price (in thousands) | $	$ 5,000
New Jersey | Building and Building Improvements
Property, Plant and Equipment [Line Items]
Number of buildings (in buildings) | bldg	2
Leaseable Square Feet (in sqft) | ft²	270,254
New Jersey | Acres of Developable Land
Property, Plant and Equipment [Line Items]
Acres of Developable Land (in acres) | a	0.0
New Jersey | Land, Buildings and Improvements
Property, Plant and Equipment [Line Items]
Purchase Price (in thousands) | $	$ 51,775
Disposal Group, Not Discontinued Operations | Building and Building Improvements
Property, Plant and Equipment [Line Items]
Number of buildings (in buildings) | bldg	4
Leaseable Square Feet (in sqft) | ft²	297,223
Disposal Group, Not Discontinued Operations | Acres of Developable Land
Property, Plant and Equipment [Line Items]
Acres of Developable Land (in acres) | a	0.8
Disposal Group, Not Discontinued Operations | Land, Buildings and Improvements
Property, Plant and Equipment [Line Items]
Gross Proceeds (in thousands) | $	$ 89,150
Disposal Group, Not Discontinued Operations | Florida | Building and Building Improvements
Property, Plant and Equipment [Line Items]
Number of buildings (in buildings) | bldg	3
Leaseable Square Feet (in sqft) | ft²	150,751
Disposal Group, Not Discontinued Operations | Florida | Acres of Developable Land
Property, Plant and Equipment [Line Items]
Acres of Developable Land (in acres) | a	0.0
Disposal Group, Not Discontinued Operations | Florida | Land, Buildings and Improvements
Property, Plant and Equipment [Line Items]
Gross Proceeds (in thousands) | $	$ 23,400
Disposal Group, Not Discontinued Operations | New Jersey | Building and Building Improvements
Property, Plant and Equipment [Line Items]
Number of buildings (in buildings) | bldg	0
Leaseable Square Feet (in sqft) | ft²	0
Disposal Group, Not Discontinued Operations | New Jersey | Acres of Developable Land
Property, Plant and Equipment [Line Items]
Acres of Developable Land (in acres) | a	0.8
Disposal Group, Not Discontinued Operations | New Jersey | Land, Buildings and Improvements
Property, Plant and Equipment [Line Items]
Gross Proceeds (in thousands) | $	$ 4,000
Disposal Group, Not Discontinued Operations | DC Metro | Building and Building Improvements
Property, Plant and Equipment [Line Items]
Number of buildings (in buildings) | bldg	1
Leaseable Square Feet (in sqft) | ft²	146,472
Disposal Group, Not Discontinued Operations | DC Metro | Acres of Developable Land
Property, Plant and Equipment [Line Items]
Acres of Developable Land (in acres) | a	0.0
Disposal Group, Not Discontinued Operations | DC Metro | Land, Buildings and Improvements
Property, Plant and Equipment [Line Items]
Gross Proceeds (in thousands) | $	$ 61,750