Real Estate Investments - Acquisitions (Details) $ in Millions				6 Months Ended
	May 13, 2016 USD ($) ft² Bed	Apr. 29, 2016 USD ($) ft² Bed	Mar. 31, 2016 USD ($) ft² Bed	Jun. 30, 2016 USD ($) ft²
Business Acquisition [Line Items]
Square footage | ft²				179,361
Real Estate				$ 78.2
Other				(2.0)
Real Estate Acquisitions [Member]
Business Acquisition [Line Items]
Purchase price				79.9
Cash consideration				63.0
Purchase price adjustments/credits				(3.7)
Capital obligations				(13.2)
Washington [Member] | Real Estate Acquisitions [Member]
Business Acquisition [Line Items]
Square footage | ft²		46,637	69,712
Purchase price		$ 21.6	$ 38.3
Cash consideration		18.8	37.7
Purchase price credits		1.5
Purchase price adjustments/credits		(2.8)	(0.6)
Acquisition costs expensed			1.6
Capital obligations		$ 0.0	$ 0.0
Number of Beds | Bed		321	281
Percentage of property leased		100.00%	100.00%
Date Acquired		Apr. 29, 2016	Mar. 31, 2016
Real Estate		$ 20.1	$ 37.7
Other		$ (1.3)	$ 0.0
CALIFORNIA | Real Estate Acquisitions [Member]
Business Acquisition [Line Items]
Square footage | ft²	63,012
Purchase price	$ 20.0
Cash consideration	6.5
Purchase price adjustments/credits	(0.3)
Capital obligations	$ (13.2)
Number of Beds | Bed	225
Percentage of property leased	80.00%
Date Acquired	May 13, 2016
Real Estate	$ 20.4
Other	(0.7)
Premium recorded at acquisition	$ 0.8			$ 0.8
Stated interest rate (percent)	4.77%