Acquisitions - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 Rate integer	Sep. 30, 2011	Dec. 31, 2011 Rate	May 31, 2011
Business Acquisition [Line Items]
General and Administrative Expense	$ 6,535,000	$ 6,412,000	$ 19,724,000	$ 18,070,000
Amortization of in-place leases	7,548,000	10,759,000	44,314,000	10,759,000
Number of sites per purchase agreements						31,167
Acres of land in which properties located					6,500
Number of states in which properties located						16
Purchase price					1,500,000,000	1,430,000,000
Acquisition Properties, revenues	42,400,000	23,900,000	125,900,000	23,900,000
Number of closed acquisition properties					75
Mortgage debt assumed for acquisition of properties, aggregate stated value					548,000,000
Number of properties used as a pledge	172		172		174
Term loan financing proceeds			0	200,000,000	200,000,000
Net proceeds from common stock offering					344,000,000
Common stock offering shares					6,037,500
New mortgage notes payable financing proceeds		200,000,000	159,500,000	200,000,000
Debt, minimum interest rate			3.90%		4.65%
Debt, maximum interest rate			8.90%		8.87%
Number of Ground Lease Sites	2,200		2,200
Escrow Deposit Shares	114,000		114,000
Unsecured Debt	200,000,000		200,000,000		200,000,000
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount			4,600,000
Escrow Deposit	6,800,000		6,800,000
Business Acquisition, Contingent Consideration, at Fair Value	500,000		500,000
Minimum
Business Acquisition [Line Items]
Debt, maturity year	2013		2013		2012
Maximum
Business Acquisition [Line Items]
Debt, maturity year	2023		2023		2023
Common Stock
Business Acquisition [Line Items]
Stock issued to acquire properties, share					1,708,276
Stock issued to acquire properties, aggregate stated value					111,000,000
Series B Subordinated Non-Voting Cumulative Redeemable Preferred Stock
Business Acquisition [Line Items]
Stock issued to acquire properties, share					1,740,000
Stock issued to acquire properties, aggregate stated value					113,000,000
Acquired Property
Business Acquisition [Line Items]
Number of properties used as a pledge					35
Manufactured homes
Business Acquisition [Line Items]
Number of portfolio agreed to purchase					75
Recreational Vehicle Resort [Member]
Business Acquisition [Line Items]
Number of portfolio agreed to purchase					1
Real Estate Investment [Member]
Business Acquisition [Line Items]
Business Acquisition, Purchase Price Allocation, Property, Plant and Equipment	1,424,700,000		1,424,700,000
Business Acquisition Pro Forma Information
Business Acquisition [Line Items]
Property, Plant and Equipment, Useful Life	1 year
Scenario, Forecast | Business Acquisition Pro Forma Information
Business Acquisition [Line Items]
Amortization of in-place leases	$ 18,300,000		$ 55,100,000