Acquisitions, Dispositions and Mortgage Repayments - Acquisitions (Details) $ in Millions																										12 Months Ended
		Dec. 18, 2015 USD ($) ft²		Nov. 18, 2015 USD ($) ft²		Nov. 03, 2015 USD ($) ft²	Oct. 23, 2015 USD ($) ft²		Sep. 14, 2015 USD ($) ft²	Sep. 01, 2015 USD ($) ft²		Aug. 21, 2015 USD ($) ft²	Jun. 26, 2015 USD ($) ft²		Jan. 15, 2015 USD ($) ft²	Dec. 01, 2014 USD ($) ft²		Oct. 29, 2014 USD ($) ft²	Sep. 16, 2014 USD ($) ft²	Jul. 28, 2014 USD ($) ft²		Jun. 06, 2014 USD ($) ft²	Jun. 04, 2014 USD ($) ft²	May. 22, 2014 USD ($) ft²	Mar. 28, 2014 USD ($) ft²	Dec. 31, 2015 USD ($) ft²		Dec. 31, 2014 USD ($) ft²
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Purchase Price																										$ 190.1
Purchase Price Adjustments/(Credits)																										(5.3)
Mortgage Notes Payable Assumed	[1]																									(28.4)
Cash Consideration	[2]																									156.4
Real Estate																										186.4
Other	[3]																									$ (1.6)
Square Footage | ft²																										504,249
Real estate acquisitions [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Purchase Price																										$ 187.2		$ 168.5
Purchase Price Adjustments/(Credits)																										(5.3)		1.0
Elimination of Mortgage Note Receivable																												(121.2)
Mortgage Notes Payable Assumed																										(28.4)	[1]	(18.2)	[4]
Cash Consideration																										153.5	[2]	69.9	[5]
Real Estate																										183.5		206.5
Other																										$ (1.6)	[3]	$ 2.6	[6]
Square Footage | ft²																										504,249		673,454
Fair value adjustments on mortgage notes payable assumed																										$ 0.4		$ 1.4
Real estate acquisitions [Member] | California [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Date Acquired						Nov. 03, 2015									Jan. 15, 2015
Purchase Price						$ 47.0									$ 39.3
Purchase Price Adjustments/(Credits)						(3.4)									(0.2)
Cash Consideration	[2]					43.6									39.1
Real Estate						44.2									39.2
Other	[3]					$ (0.6)									$ (0.1)
Square Footage | ft²						99,942									110,679
Real estate acquisitions [Member] | Colorado [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Date Acquired									Sep. 14, 2015
Purchase Price									$ 6.5
Purchase Price Adjustments/(Credits)									(0.3)
Cash Consideration	[2]								6.2
Real Estate									6.3
Other	[3]								$ (0.1)
Square Footage | ft²									47,508
Real estate acquisitions [Member] | Florida [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Date Acquired																			Sep. 16, 2014
Purchase Price																			$ 7.9
Purchase Price Adjustments/(Credits)																			(0.1)
Cash Consideration	[5]																		7.8
Real Estate																			7.9
Other	[6]																		$ (0.1)
Square Footage | ft²																			47,962
Real estate acquisitions [Member] | Iowa [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Date Acquired																									Mar. 28, 2014
Purchase Price Adjustments/(Credits)																									$ 0.2
Elimination of Mortgage Note Receivable																									(40.0)
Real Estate																									40.2
Other	[6]																								$ (0.4)
Square Footage | ft²																									152,655
Real estate acquisitions [Member] | Minnesota [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Date Acquired		Dec. 18, 2015																		Jul. 28, 2014
Purchase Price		$ 16.0																		$ 19.8
Purchase Price Adjustments/(Credits)		0.1																		0.8
Mortgage Notes Payable Assumed		(9.5)	[1]																	(11.4)	[4]
Cash Consideration		6.6	[2]																	9.2	[5]
Real Estate		16.0																		20.9
Other		$ 0.1	[3]																	$ (0.3)	[6]
Square Footage | ft²		64,143																		60,476
Fair value adjustments on mortgage notes payable assumed		$ 0.1																		$ 1.0
Real estate acquisitions [Member] | North Carolina [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Date Acquired																						Jun. 06, 2014
Purchase Price																						$ 6.5
Cash Consideration	[5]																					6.5
Real Estate																						$ 6.5
Square Footage | ft²																						35,292
Real estate acquisitions [Member] | Oklahoma [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Date Acquired																		Oct. 29, 2014						May 22, 2014
Purchase Price																		$ 17.5						$ 85.4
Purchase Price Adjustments/(Credits)																		0.1						(0.1)
Elimination of Mortgage Note Receivable																								(81.2)
Mortgage Notes Payable Assumed	[4]																	(6.8)
Cash Consideration	[5]																	10.8						4.1
Real Estate																		17.9						85.4
Other	[6]																	$ (0.3)						$ (0.1)
Square Footage | ft²																		68,860						200,000
Fair value adjustments on mortgage notes payable assumed																		$ 0.4
Real estate acquisitions [Member] | Tennessee [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Purchase Price												$ 2.0
Square Footage | ft²												7,672
Real estate acquisitions [Member] | Texas [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Date Acquired																							Jun. 04, 2014
Purchase Price																							$ 8.7
Purchase Price Adjustments/(Credits)																							0.1
Cash Consideration	[5]																						8.8
Real Estate																							8.8
Other	[6]																						$ 0.0
Square Footage | ft²																							48,048
Real estate acquisitions [Member] | Washington [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Date Acquired				Nov. 18, 2015			Oct. 23, 2015			Sep. 01, 2015			Jun. 26, 2015			Dec. 01, 2014
Purchase Price				$ 27.6			$ 8.8			$ 28.0			$ 14.0			$ 22.7
Purchase Price Adjustments/(Credits)				0.1			(1.3)			(0.2)			(0.1)
Mortgage Notes Payable Assumed	[1]									(9.4)			(9.5)
Cash Consideration				27.7	[2]		7.5	[2]		18.4	[2]		4.4	[2]		22.7	[5]
Real Estate				27.6			8.6			27.8			13.8			18.9
Other				$ 0.1	[3]		$ (1.1)	[3]		$ 0.0	[3]		$ 0.1	[3]		$ 3.8	[6]
Square Footage | ft²				60,437			33,169			52,813			35,558			60,161
Fair value adjustments on mortgage notes payable assumed										$ 0.3			$ 0.2
Land acquisitions [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Purchase Price																										2.9
Cash Consideration	[2]																									2.9
Real Estate																										$ 2.9

[1] The mortgage notes payable assumed in the acquisitions do not reflect the fair value adjustments totaling $0.4 million recorded by the Company upon acquisition (included in Other).

[2] Cash consideration excludes prorations of revenue and expense due to/from seller at the time of the acquisition.

[3] Includes assets acquired, liabilities assumed, intangibles recognized at acquisition and fair value adjustments on debt assumed.

[4] The mortgage notes payable assumed in the acquisitions do not reflect the fair value adjustments totaling $1.4 million recorded by the Company upon acquisition (included in Other).

[5] Cash consideration excludes non-real estate assets acquired and liabilities assumed in the acquisitions.

[6] Includes intangibles recognized at acquisition and fair value adjustments on debt assumed.