Acquisitions, Dispositions and Mortgage Repayments - Additional information (Details) $ in Millions																										3 Months Ended		12 Months Ended
	Dec. 22, 2016 USD ($) ft²	Dec. 21, 2016 USD ($) ft²	Dec. 20, 2016 USD ($) ft²	Oct. 28, 2016 USD ($) ft²	Oct. 17, 2016 USD ($) ft²	Sep. 12, 2016 USD ($) ft²	May 13, 2016 USD ($) ft²	Apr. 29, 2016 USD ($) ft²	Mar. 31, 2016 USD ($) ft²	Dec. 18, 2015 USD ($) ft²	Dec. 14, 2015 USD ($) ft²	Nov. 18, 2015 USD ($) ft²	Nov. 05, 2015 USD ($) ft²	Nov. 03, 2015 USD ($) ft²	Oct. 23, 2015 USD ($) ft²	Sep. 30, 2015 USD ($) ft²	Sep. 25, 2015 USD ($) ft²	Sep. 16, 2015 USD ($) ft²	Sep. 14, 2015 USD ($) ft²	Sep. 01, 2015 USD ($) ft²	Jul. 17, 2015 USD ($) ft²	Jun. 30, 2015 USD ($) ft² property	Jun. 26, 2015 USD ($) ft²	May 21, 2015 USD ($) ft²	Jan. 15, 2015 USD ($) ft²	Sep. 30, 2015 USD ($) ft² property	Jun. 30, 2015 USD ($) ft² property	Dec. 31, 2016 USD ($) ft² property	Dec. 31, 2015 USD ($) ft² property land_parcel
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Number of properties acquired | property																												10	8
Number of land parcels acquired | land_parcel																													2
Number of properties sold | property																										1	2	6	2
Square Footage | ft²																												583,011	504,249
Purchase Price																													$ 190.1
Cash Consideration																													156.4
Mortgage Notes Payable Assumed																													28.4
Fair value discount																												$ (1.2)	$ (1.6)
Area Covered Under Real Estate Investment Sold in Measurement Units | ft²																												320,702
Real Estate Investment Net Disposed of During Period																												$ 49.4
Disposition Sales Price																												94.7
Gain (loss) on disposition of property																												41.0
Proceeds from sale of cost method investment in real estate																												93.3
Closing Adjustments																												(1.4)
Real estate dispositions [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Area Covered Under Real Estate Investment Sold in Measurement Units | ft²																													534,074
Real Estate Investment Net Disposed of During Period																													$ 82.9
Disposition Sales Price																													158.0
Gain (loss) on disposition of property																													66.9
Proceeds from sale of cost method investment in real estate																													153.1
Closing Adjustments																													(4.9)
Mortgage note repayments [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Company-financed mortgage notes																													$ 1.9
Real estate acquisitions [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Square Footage | ft²																													504,249
Purchase Price																												241.9	$ 187.2
Cash Consideration																												224.9	153.5
Purchase price credits																												1.0	2.3
Capital commitments																												2.8	3.0
Mortgage Notes Payable Assumed																												13.2	28.4
Notes Assumed, Unamortized Premium																													0.4
Fair value discount																													$ (1.6)
California [Member] | Real estate acquisitions [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Square Footage | ft²							63,012							99,942											110,679
Purchase Price							$ 20.0							$ 47.0											$ 39.3
Cash Consideration							6.5							43.6											39.1
Mortgage Notes Payable Assumed							13.2
Notes Assumed, Unamortized Premium																												$ 0.8
Fair value discount							$ (0.7)							$ (0.6)											$ (0.1)
Washington [Member] | Real estate acquisitions [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Square Footage | ft²		20,740			29,753	87,462		46,637	69,712			60,437			33,169					52,813			35,558
Purchase Price		$ 5.1			$ 9.8	$ 53.1		$ 21.6	$ 38.3			$ 27.6			$ 8.8					$ 28.0			$ 14.0
Cash Consideration		5.1			9.8	53.0		18.8	37.7			27.7			7.5					18.4			4.4
Mortgage Notes Payable Assumed		0.0			0.0	0.0		0.0	0.0											9.4			9.5
Fair value discount		$ (0.1)			$ (0.1)	$ (1.6)		$ (1.3)	$ 0.0			$ 0.1			$ (1.1)					$ 0.0			$ 0.1
Tennessee [Member] | Real estate dispositions [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Area Covered Under Real Estate Investment Sold in Measurement Units | ft²	8,749			45,274
Real Estate Investment Net Disposed of During Period	$ 1.8			$ 6.3
Disposition Sales Price	2.8			8.8
Gain (loss) on disposition of property	0.8			2.1
Proceeds from sale of cost method investment in real estate	2.6			8.6
Closing Adjustments	$ (0.2)			$ (0.2)
Colorado [Member] | Real estate acquisitions [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Square Footage | ft²																			47,508
Purchase Price																			$ 6.5
Cash Consideration																			6.2
Fair value discount																			$ (0.1)
Virginia [Member] | Real estate dispositions [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Area Covered Under Real Estate Investment Sold in Measurement Units | ft²																								5,323
Real Estate Investment Net Disposed of During Period																								$ 0.3
Disposition Sales Price																								1.0
Gain (loss) on disposition of property																								0.7
Proceeds from sale of cost method investment in real estate																								1.0
Closing Adjustments																								$ 0.0
Minnesota [Member] | Real estate acquisitions [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Square Footage | ft²		48,281								64,143
Purchase Price		$ 12.6								$ 16.0
Cash Consideration		12.5								6.6
Mortgage Notes Payable Assumed		0.0								9.5
Fair value discount		$ 1.2								$ 0.1
Florida [Member] | Real estate dispositions [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Area Covered Under Real Estate Investment Sold in Measurement Units | ft²																		119,903
Real Estate Investment Net Disposed of During Period																		$ 10.5
Disposition Sales Price																		16.3
Gain (loss) on disposition of property																		5.1
Proceeds from sale of cost method investment in real estate																		15.8
Closing Adjustments																		$ (0.5)
Indiana [Member] | Real estate dispositions [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Number of properties sold | property																						2
Area Covered Under Real Estate Investment Sold in Measurement Units | ft²																						175,999					175,999
Real Estate Investment Net Disposed of During Period																						$ 50.5					$ 50.5
Disposition Sales Price																						97.0					97.0
Gain (loss) on disposition of property																						40.9
Proceeds from sale of cost method investment in real estate																						93.3
Closing Adjustments																						$ (3.7)					$ (3.7)
Pennsylvania [Member] | Real estate dispositions [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Area Covered Under Real Estate Investment Sold in Measurement Units | ft²																					63,914
Real Estate Investment Net Disposed of During Period																					$ 7.4
Disposition Sales Price																					18.4
Gain (loss) on disposition of property																					10.6
Proceeds from sale of cost method investment in real estate																					18.4
Closing Adjustments																					$ 0.0
Arizona [Member] | Real estate dispositions [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Area Covered Under Real Estate Investment Sold in Measurement Units | ft²			51,903										56,645				40,782
Real Estate Investment Net Disposed of During Period			$ 13.5										$ 4.9				$ 2.0
Disposition Sales Price			22.3										5.3				3.0
Gain (loss) on disposition of property			7.4										0.1				0.8
Proceeds from sale of cost method investment in real estate			22.3										5.0				$ 3.0
Closing Adjustments			$ 0.0										$ (0.3)
Missouri [Member] | Real estate dispositions [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Area Covered Under Real Estate Investment Sold in Measurement Units | ft²																13,478										13,478
Real Estate Investment Net Disposed of During Period																$ 2.9										$ 2.9
Disposition Sales Price																3.0										3.0
Gain (loss) on disposition of property																(0.3)
Proceeds from sale of cost method investment in real estate																2.8
Closing Adjustments																$ (0.2)										$ (0.2)
Georgia [Member] | Real estate dispositions [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Area Covered Under Real Estate Investment Sold in Measurement Units | ft²											58,030
Real Estate Investment Net Disposed of During Period											$ 4.4
Disposition Sales Price											14.0
Gain (loss) on disposition of property											9.0
Proceeds from sale of cost method investment in real estate											13.8
Closing Adjustments											$ (0.2)
Medical Office Building [Member] | Real estate dispositions [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Number of properties sold | property																													8
Surgical Facility [Member] | Real estate dispositions [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Number of properties sold | property																													1