Real Estate Assets - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended		0 Months Ended		0 Months Ended		3 Months Ended	12 Months Ended			3 Months Ended	12 Months Ended	3 Months Ended	9 Months Ended
	Sep. 30, 2014 Property	Sep. 30, 2013	Sep. 30, 2014 Property	Sep. 30, 2013	Jul. 10, 2014 Massachusetts Property	Jul. 10, 2014 Massachusetts Property	Jul. 10, 2014 Massachusetts Directors, Executive Officers and Related Interests	Jul. 10, 2014 Massachusetts Directors, Executive Officers and Related Interests	Sep. 30, 2014 Reinvestment Projects Completed Investment	Dec. 31, 2013 Reinvestment Projects Completed Investment	Dec. 31, 2013 Reinvestment Projects Completed California Property	Sep. 30, 2014 Reinvestment Projects Completed California, Pennsylvania, Texas and Indiana Property	Sep. 30, 2014 Construction in Progress	Dec. 31, 2013 Construction in Progress	Sep. 30, 2014 Series of Individually Immaterial Business Acquisitions	Sep. 30, 2014 Series of Individually Immaterial Business Acquisitions
Real Estate Properties [Line Items]
Number of properties acquired	313		313			3					1	6
Number of land parcels acquired					2
Property acquired purchase price					$ 94.3
Percentage of equity interest in sellers properties								50.00%
Gross economic interest in sellers properties							47.1
Revenues															7.5	13.5
Net Income															4.5	7.2
Acquisition costs	0.7		2.4
Number of real estate property disposed	5		7
Property sold	0.8		1.4
Net loss on sale of properties	(2.4)		(2.5)
Weighted-average interest rate on all outstanding debt	6.00%		6.00%
Capitalized interest	$ 0.2	$ 0.2	$ 0.5	$ 0.4									$ 0.7	$ 0.8
Number of completed investment projects placed into services									6	1