Borrowing Arrangements - Additional Information (Detail) (USD $)	3 Months Ended			6 Months Ended			6 Months Ended	1 Months Ended		0 Months Ended	1 Months Ended	0 Months Ended			1 Months Ended	0 Months Ended					1 Months Ended				1 Months Ended		1 Months Ended	6 Months Ended			1 Months Ended
	Jun. 30, 2013 Rate integer	Sep. 30, 2012	Jun. 30, 2012	Jun. 30, 2013 Rate integer	Jun. 30, 2012	Dec. 31, 2012	Jun. 30, 2013 Old Credit Facilities [Member]	Jul. 31, 2012 Amended Line of Credit Facility	Jun. 30, 2013 New Credit Facilities [Member]	Jul. 30, 2013 Subsequent Event [Member]	Aug. 30, 2013 Subsequent Event [Member]	Jul. 30, 2013 Subsequent Event [Member]	Jul. 15, 2013 Subsequent Event [Member]	Jul. 30, 2013 Subsequent Event [Member] Old Credit Facilities [Member]	Aug. 30, 2013 Subsequent Event [Member] Old Credit Facilities [Member]	Jul. 30, 2013 Subsequent Event [Member] Old Credit Facilities [Member]	Jul. 15, 2013 Subsequent Event [Member] Old Credit Facilities [Member]	Aug. 01, 2013 Subsequent Event [Member] Old Credit Facilities [Member]	Jul. 18, 2013 Subsequent Event [Member] Old Credit Facilities [Member]	Jul. 02, 2013 Subsequent Event [Member] Old Credit Facilities [Member]	Aug. 30, 2013 Subsequent Event [Member] New Credit Facilities [Member]	Aug. 01, 2013 Subsequent Event [Member] New Credit Facilities [Member]	Jul. 30, 2013 Subsequent Event [Member] New Credit Facilities [Member]	Jun. 30, 2013 Minimum	Jul. 31, 2012 Minimum Amended Line of Credit Facility Rate	Jun. 30, 2013 Maximum	Jul. 31, 2012 Maximum Amended Line of Credit Facility Rate	Jun. 30, 2013 Term Loans	Jun. 30, 2013 Term Loans Minimum Rate	Jun. 30, 2013 Term Loans Maximum Rate	Aug. 30, 2013 Manufactured Home [Member] Subsequent Event [Member] Old Credit Facilities [Member]	Aug. 01, 2013 Manufactured Home [Member] Subsequent Event [Member] Old Credit Facilities [Member]	Aug. 01, 2013 Manufactured Home [Member] Subsequent Event [Member] New Credit Facilities [Member]	Jun. 30, 2013 Segment, Discontinued Operations [Member]	Dec. 31, 2012 Segment, Discontinued Operations [Member]
Debt Instrument [Line Items]
Mortgage notes payable	$ 2,122,883,000			$ 2,122,883,000		$ 2,061,610,000			$ 110,000,000													$ 115,000,000	$ 70,500,000										$ 166,600,000	$ 8,163,000	$ 8,256,000
Debt Instrument, Unamortized Premium																																		400,000
Mortgage notes payable, weighted average interest rate	5.50%			5.50%
Debt, minimum interest rate				3.90%
Debt, maximum interest rate				8.90%
Debt, maturity year									2023					2015		2015		2013	2020	2015		2028	2038	2013		2023						2015	2038
Number of pledge properties	177			177		170	4							3		3			1	6		7	2									18
Carrying values of properties encumbered	2,547,000,000			2,547,000,000		2,485,000,000
Debt, maturity date																												Jun. 30, 2017
Repayments of Long-term Debt							29,800,000							20,900,000	60,700,000	7,800,000	120,000,000														154,500,000
Debt Instrument, Interest Rate, Stated Percentage							5.70%		4.87%					6.30%		6.30%		6.02%	7.20%	5.70%		4.25%	4.35%									5.56%
Payments of Debt Extinguishment Costs	(1,381,000)		0	(1,381,000)	0					(2,800,000)	(18,900,000)	(1,450,000)	(15,000,000)
Mortgage Loans on Real Estate, Number of Loans																					5
Debt instrument face amount																												200,000,000
Debt, extension option period																												1 year
Debt instrument, interest rate based on margin over LIBOR																									1.40%		2.00%		1.85%	2.80%
Start date to repay debt without penalty on prepayment																												Jul. 01, 2014
Debt, percentage of prepayment penalty																												2.00%
LIBOR Swap Agreement, period																												3 years
Lines of credit, borrowing capacity	380,000,000			380,000,000		380,000,000
Lines of credit, maturity date								Sep. 15, 2016
Line of credit facility, interest rate based on margin over LIBOR				Our amended LOC bears a LIBOR rate plus a maximum of 1.40% to 2.00%, contains a 0.25% to 0.40% facility rate and has a maturity date of September 15, 2016. We have a one year extension option under our LOC.
Lines of credit, extension option								1 year
Line of Credit Facility, Commitment Fee Amount		$ 1,300,000
Line of credit, facility rate																									0.25%		0.40%