Acquisitions, Dispositions and Mortgage Repayments - Dispositions (Details) $ in Millions																					3 Months Ended		12 Months Ended
		Dec. 14, 2015 USD ($) ft²	Nov. 05, 2015 USD ($) ft²	Sep. 30, 2015 USD ($) ft²	Sep. 25, 2015 USD ($) ft²	Sep. 16, 2015 USD ($) ft²	Jul. 17, 2015 USD ($) ft²	Jun. 30, 2015 USD ($) ft² property	May. 21, 2015 USD ($) ft²	Dec. 29, 2014 USD ($) ft²	Dec. 18, 2014 USD ($) ft²	[1]	Nov. 25, 2014 USD ($) ft²		Nov. 14, 2014 USD ($) ft²	Sep. 12, 2014 USD ($) ft²	Apr. 23, 2014 USD ($) ft²		Apr. 11, 2014 USD ($) ft²	[1]	Dec. 31, 2015 USD ($) ft² property	Sep. 30, 2015 USD ($) ft² property	Dec. 31, 2015 USD ($) ft² property	Dec. 31, 2014 USD ($) ft² property
Real Estate Dispositions [Line Items]
Sales Price																					$ 158.0		$ 158.0	$ 34.9
Closing Adjustments																					(4.9)		(4.9)	(0.7)
Mortgage Notes																					1.9		1.9	3.0
Net Proceeds																							155.0	37.2
Net Real Estate Investment																					82.9		82.9	28.2
Other (including receivables)																					$ 3.3		3.3	0.5
Gain/ (Impairment)																							$ 66.9	$ 5.5
Square Footage | ft²																					534,074		534,074	476,536
Number of properties sold | property																					2	1	2	2
Real estate dispositions [Member]
Real Estate Dispositions [Line Items]
Sales Price																					$ 158.0		$ 158.0	$ 34.9
Closing Adjustments																					(4.9)		(4.9)	(0.7)
Mortgage Notes																					0.0		0.0	(1.9)
Net Proceeds																							153.1	32.3
Net Real Estate Investment																					82.9		82.9	28.2
Other (including receivables)																					$ 3.3		3.3	0.5
Gain/ (Impairment)																							$ 66.9	$ 5.5
Square Footage | ft²																					534,074		534,074	476,536
Mortgage note repayments [Member]
Real Estate Dispositions [Line Items]
Mortgage Notes																					$ 1.9		$ 1.9	$ 4.9
Net Proceeds																							$ 1.9	$ 4.9
Arizona [Member] | Real estate dispositions [Member]
Real Estate Dispositions [Line Items]
Date Disposed			Nov. 05, 2015		Sep. 25, 2015
Sales Price			$ 5.3		$ 3.0
Closing Adjustments			(0.3)
Net Proceeds			5.0		3.0
Net Real Estate Investment			4.9		2.0
Other (including receivables)					0.2
Gain/ (Impairment)			$ 0.1		$ 0.8
Square Footage | ft²			56,645		40,782
Florida [Member] | Real estate dispositions [Member]
Real Estate Dispositions [Line Items]
Date Disposed						Sep. 16, 2015													Apr. 11, 2014
Sales Price						$ 16.3													$ 1.8
Closing Adjustments						(0.5)													(0.1)
Net Proceeds						15.8													1.7
Net Real Estate Investment						10.5													$ 1.7
Other (including receivables)						0.2
Gain/ (Impairment)						$ 5.1
Square Footage | ft²						119,903													52,608
Georgia [Member] | Real estate dispositions [Member]
Real Estate Dispositions [Line Items]
Date Disposed		Dec. 14, 2015
Sales Price		$ 14.0
Closing Adjustments		(0.2)
Net Proceeds		13.8
Net Real Estate Investment		4.4
Other (including receivables)		0.4
Gain/ (Impairment)		$ 9.0
Square Footage | ft²		58,030
Illinois [Member] | Real estate dispositions [Member]
Real Estate Dispositions [Line Items]
Date Disposed	[1]									Dec. 29, 2014
Sales Price	[1]									$ 0.5
Net Proceeds	[1]									0.5
Net Real Estate Investment	[1]									0.8
Gain/ (Impairment)	[1]									$ (0.3)
Square Footage | ft²	[1]									110,000
Indiana [Member] | Real estate dispositions [Member]
Real Estate Dispositions [Line Items]
Date Disposed	[2]							Jun. 30, 2015
Sales Price	[2]							$ 97.0
Closing Adjustments	[2]							(3.7)
Net Proceeds	[2]							93.3
Net Real Estate Investment	[2]							50.5
Other (including receivables)	[2]							1.9
Gain/ (Impairment)	[2]							$ 40.9
Square Footage | ft²	[2]							175,999
Number of properties sold | property								2
Missouri [Member] | Real estate dispositions [Member]
Real Estate Dispositions [Line Items]
Date Disposed				Sep. 30, 2015							Dec. 18, 2014
Sales Price				$ 3.0							$ 1.3											$ 3.0
Closing Adjustments				(0.2)																		(0.2)
Net Proceeds				2.8							1.3
Net Real Estate Investment				2.9							1.4											2.9
Other (including receivables)				0.2							0.1											$ 0.2
Gain/ (Impairment)				$ (0.3)							$ (0.2)
Square Footage | ft²				13,478							26,166											13,478
Nevada [Member] | Real estate dispositions [Member]
Real Estate Dispositions [Line Items]
Date Disposed																Sep. 12, 2014
Sales Price																$ 2.3
Closing Adjustments																(0.2)
Mortgage Notes																(1.9)
Net Proceeds																0.2
Net Real Estate Investment																4.9
Gain/ (Impairment)																$ (2.8)
Square Footage | ft²																31,026
Pennsylvania [Member] | Real estate dispositions [Member]
Real Estate Dispositions [Line Items]
Date Disposed	[3]						Jul. 17, 2015
Sales Price	[3]						$ 18.4
Closing Adjustments	[3]						0.0
Mortgage Notes	[3]						0.0
Net Proceeds	[3]						18.4
Net Real Estate Investment	[3]						7.4
Other (including receivables)	[3]						0.4
Gain/ (Impairment)	[3]						$ 10.6
Square Footage | ft²	[3]						63,914
Tennessee [Member] | Real estate dispositions [Member]
Real Estate Dispositions [Line Items]
Date Disposed	[4]														Nov. 14, 2014
Sales Price	[4]														$ 3.1
Closing Adjustments	[4]														(0.2)
Net Proceeds	[4]														2.9
Net Real Estate Investment	[4]														3.2
Other (including receivables)	[4]														0.1
Gain/ (Impairment)	[4]														$ (0.4)
Square Footage | ft²	[4]														32,204
Texas [Member] | Real estate dispositions [Member]
Real Estate Dispositions [Line Items]
Date Disposed													Nov. 25, 2014	[4]			Apr. 23, 2014	[1]
Sales Price													$ 21.5	[4]			$ 4.4	[1]
Closing Adjustments	[1]																(0.2)
Net Proceeds													21.5	[4]			4.2	[1]
Net Real Estate Investment													12.1	[4]			4.1	[1]
Other (including receivables)													0.2	[4]			$ 0.1	[1]
Gain/ (Impairment)	[4]												$ 9.2
Square Footage | ft²													166,167	[4]			58,365	[1]
Virginia [Member] | Real estate dispositions [Member]
Real Estate Dispositions [Line Items]
Date Disposed									May 21, 2015
Sales Price									$ 1.0
Closing Adjustments									0.0
Net Proceeds									1.0
Net Real Estate Investment									0.3
Gain/ (Impairment)									$ 0.7
Square Footage | ft²									5,323

[1] Previously included in assets held for sale.

[2] Includes two properties.

[3] Previously included in assets held for sale.

[4] Includes two properties.