Real Estate Investments - Dispositions (Details) $ in Millions								1 Months Ended	3 Months Ended		9 Months Ended
	Sep. 07, 2017 USD ($) ft²	Jun. 29, 2017 USD ($) ft²	Jun. 16, 2017 USD ($) ft²	Mar. 31, 2017 USD ($)	Mar. 30, 2017 USD ($) ft²	Mar. 07, 2017 USD ($) ft²	Mar. 06, 2017 USD ($) ft²	Oct. 31, 2017 USD ($) building Purchase_options	Sep. 30, 2017 USD ($) ft²	Mar. 31, 2017 USD ($)	Sep. 30, 2017 USD ($) ft² property
Real Estate Dispositions [Line Items]
Number of potential dispositions | property											5
Real Estate Dispositions
Real Estate Dispositions [Line Items]
Sales price									$ 122.7		$ 122.7
Closing Adjustments									(3.3)		(3.3)
Net proceeds											119.4
Net Real Estate Investment									78.2		78.2
Other (including receivables)(3)									$ 6.8		6.8
Gain/(Impairment)											$ 34.4
Square footage | ft²									416,481		416,481
Real Estate Dispositions | INDIANA
Real Estate Dispositions [Line Items]
Date Disposed							Mar. 06, 2017
Sales price							$ 6.4
Closing Adjustments							0.0
Net proceeds							6.4
Net Real Estate Investment							1.1
Other (including receivables)(3)							0.0
Gain/(Impairment)							$ 5.3
Square footage | ft²							29,500
Real Estate Dispositions | GEORGIA
Real Estate Dispositions [Line Items]
Date Disposed						Mar. 07, 2017
Sales price						$ 0.6
Closing Adjustments						0.0
Net proceeds						0.6
Net Real Estate Investment						0.6
Other (including receivables)(3)						0.0
Gain/(Impairment)						$ 0.0
Square footage | ft²						12,000
Real Estate Dispositions | NEVADA
Real Estate Dispositions [Line Items]
Date Disposed					Mar. 30, 2017
Sales price					$ 5.5
Closing Adjustments					(0.7)
Net proceeds					4.8
Net Real Estate Investment					2.2
Other (including receivables)(3)					0.3
Gain/(Impairment)					$ 2.3
Square footage | ft²					18,147
Real Estate Dispositions | TEXAS
Real Estate Dispositions [Line Items]
Date Disposed		Jun. 29, 2017		Mar. 31, 2017
Sales price		$ 14.5							$ 69.5		$ 69.5
Closing Adjustments		(0.2)							(1.6)		(1.6)
Net proceeds		14.3		$ 67.9
Net Real Estate Investment		5.1							46.9		46.9
Other (including receivables)(3)		0.9							$ 5.2		$ 5.2
Gain/(Impairment)		$ 8.3		$ 15.8
Square footage | ft²		39,786							169,722		169,722
Real Estate Dispositions | ILLINOIS
Real Estate Dispositions [Line Items]
Date Disposed			Jun. 16, 2017
Sales price			$ 0.5
Closing Adjustments			(0.1)
Net proceeds			0.4
Net Real Estate Investment			0.4
Other (including receivables)(3)			0.0
Gain/(Impairment)			$ 0.0
Square footage | ft²			5,100
Impairment charge										$ 0.3
Real Estate Dispositions | OREGON
Real Estate Dispositions [Line Items]
Date Disposed		Jun. 29, 2017
Sales price		$ 23.2
Closing Adjustments		(0.6)
Net proceeds		22.6
Net Real Estate Investment		14.5
Other (including receivables)(3)		0.3
Gain/(Impairment)		$ 7.8
Square footage | ft²		62,246
Real Estate Dispositions | MISSOURI
Real Estate Dispositions [Line Items]
Date Disposed	Sep. 07, 2017
Sales price	$ 2.5
Closing Adjustments	(0.1)
Net proceeds	2.4
Net Real Estate Investment	7.4
Other (including receivables)(3)	0.1
Gain/(Impairment)	$ (5.1)								$ 5.1
Square footage | ft²	79,980
Potential Real Estate Disposition | VIRGINIA
Real Estate Dispositions [Line Items]
Net Real Estate Investment									$ 24.0		$ 24.0
Potential Disposition | VIRGINIA
Real Estate Dispositions [Line Items]
Sales price								$ 45.2
Number of potential dispositions | building								7
Number of Purchase Options | Purchase_options								1
Medical Office Building | ILLINOIS
Real Estate Dispositions [Line Items]
Impairment charge										$ 0.3
Medical Office Building | Potential Disposition | VIRGINIA
Real Estate Dispositions [Line Items]
Number of potential dispositions | building								5