Debt (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Debt Instrument [Line Items]
Debt	$ 2,509,846,000		$ 2,509,846,000		$ 2,398,625,000
Less current portion	410,581,000		410,581,000		47,654,000
Long-term debt	2,099,265,000		2,099,265,000		2,350,971,000
Current Portion of Mortgage Loans	359,900,000		359,900,000
Current Portion of Mortgage Loans with Extension Options	205,600,000		205,600,000
Minimum Term of Debt Extension (in years)	5		5
Maximum Term of Debt Extension (in years)	7		7
Derivative [Line Items]
Change in fair value of derivatives and amortization	(278,000)	(2,635,000)	(511,000)	(2,643,000)
Credit Facility 2011 [Member]
Debt Instrument [Line Items]
Maturity date			Jan. 31, 2016
Line of Credit Facility [Line Items]
Commitment on Prior borrowing facility	120,000,000		120,000,000
Initial commitment	200,000,000		200,000,000
Credit Facility, maximum borrowing capacity	230,000,000		230,000,000
Maturity date			Jan. 31, 2016
Description of applicable margin calculation based on utilization percentage			Amounts drawn under the facility bear interest at 90-day LIBOR plus an applicable margin, as described below. For purposes of determining the interest rate, in no event will LIBOR be less than 2.0%. The applicable margin varies with the percentage of the total commitment drawn, with a 4.5% margin at 35% or lower utilization, a 5.0% margin at utilization greater than 35% but less than or equal to 50%, and a 5.5% margin at greater than 50% utilization. The Company is also required to pay a quarterly commitment fee of 1.0% per annum on the unused portion of the facility.
Quarterly commitment fee (in hundredths)			1.00%
Availability under the secured line of credit	201,700,000		201,700,000
Line of credit borrowings outstanding	75,000,000		75,000,000
Secured and unsecured letter of credit facilities
Line of Credit Facility [Line Items]
Credit Facility, maximum borrowing capacity	92,700,000		92,700,000
Letters of credit outstanding	78,300,000		78,300,000
First mortgage loan issued in January 2012 [Member]
Debt Instrument [Line Items]
Maturity date			Jan. 31, 2017
Line of Credit Facility [Line Items]
Maturity date			Jan. 31, 2017
Principal amount of note	63,000,000		63,000,000
Interest rate terms			The loan bears interest at a variable rate equal to 30-day LIBOR plus a margin of 300 basis points
Extinguishment of debt with proceeds of debt			62,800,000
First mortgage loan issued in February 2012 [Member]
Debt Instrument [Line Items]
Maturity date			Feb. 28, 2017
Line of Credit Facility [Line Items]
Maturity date			Feb. 28, 2017
Principal amount of note	20,000,000		20,000,000
Interest rate terms			The loan bears interest at a variable rate equal to 30-day LIBOR plus a margin of 275 basis points
Mortgage Loan Issued to Finance Acquisition [Member]
Line of Credit Facility [Line Items]
Principal amount of note	77,900,000		77,900,000
Interest rate terms			75% of the facility bears interest at a fixed rate of 4.2% and the remaining 25% of the facility bears interest at a variable rate of 30-day LIBOR plus a margin of 276 basis points
Percentage of loans bearing interest at a fixed rate (in hundredths)	75.00%		75.00%
Percentage of loans bearing interest at a variable rate (in hundredths)	25.00%		25.00%
Term of loan (in years)	10		10
Number of facilities purchased	9		9
Seller-Financed Debt [Member]
Line of Credit Facility [Line Items]
Principal amount of note	15,000,000		15,000,000
Interest rate terms			bears interest at a fixed rate of 7.0%
Term of loan (in years)	2		2
Number of facilities purchased	9		9
First mortgage loan issued in June 2012 [Member]
Debt Instrument [Line Items]
Maturity date			Jun. 30, 2017
Line of Credit Facility [Line Items]
Maturity date			Jun. 30, 2017
Principal amount of note	15,000,000		15,000,000
Interest rate terms			The loan bears interest at a variable rate equal to 30-day LIBOR plus a margin of 425 basis points
Extinguishment of debt with proceeds of debt			15,000,000
Number of communities securing debt (in number of communities)			2
Interest Rate Swap [Member]
Derivative [Line Items]
Current notional balance	27,568,000		27,568,000
Highest possible notional	27,568,000		27,568,000
Lowest interest rate (in hundredths)	5.49%		5.49%
Highest interest rate (in hundredths)	5.49%		5.49%
Average fixed rate	5.49%		5.49%
Earliest maturity date	2016		2016
Latest maturity date	2016		2016
Weighted average original maturity	5.0 years		5.0 years
Estimated liability fair value (included in other liabilities)	(1,944,000)		(1,944,000)		(2,809,000)
Number of swaps agreements terminated			1
Notional amount of swap agreement terminated	150,000,000		150,000,000
Cash collateral paid to counterparties pursuant to swap termination			1,200,000
Interest Rate Cap [Member]
Derivative [Line Items]
Current notional balance	418,238,000		418,238,000
Highest possible notional	418,238,000		418,238,000
Lowest interest rate (in hundredths)	5.00%		5.00%
Highest interest rate (in hundredths)	6.06%		6.06%
Average fixed rate	5.49%		5.49%
Earliest maturity date	2012		2012
Latest maturity date	2017		2017
Weighted average original maturity	2.7 years		2.7 years
Estimated asset fair value (included in other assets)	0		0		0
Number of cap agreements entered	2		2
Notional amount of new agreements	169,500,000		169,500,000
Mortgages Payable [Member]
Debt Instrument [Line Items]
Debt	1,568,697,000		1,568,697,000		1,470,462,000
Maturity date, start			2013
Maturity date, end			2022
Weighted average interest rate (in hundredths)	4.87%		4.87%		5.04%
Unamortized debt discount	500,000		500,000
$150 Million Series A Notes Payable [Member]
Debt Instrument [Line Items]
Debt	146,503,000		146,503,000		148,601,000
Maturity date			Aug. 31, 2013
Number of communities securing debt (in number of communities)			5
Amount of cash collateral securing debt			3,000,000
Description of variable rate basis			LIBOR plus 0.88%
Basis spread on variable rate basis (in hundredths)	0.88%		0.88%
Line of Credit Facility [Line Items]
Maturity date			Aug. 31, 2013
Discount Mortgage Note payable due June 2013 [Member]
Debt Instrument [Line Items]
Debt	80,224,000		80,224,000		79,911,000
Maturity date			Jun. 30, 2013
Weighted average interest rate (in hundredths)	2.58%		2.58%		2.52%
Unamortized debt discount	2,000,000		2,000,000
Line of Credit Facility [Line Items]
Maturity date			Jun. 30, 2013
Variable rate tax exempt bonds [Member]
Debt Instrument [Line Items]
Debt	100,186,000		100,186,000		100,423,000
Maturity date			Dec. 31, 2032
Weighted average interest rate (in hundredths)	1.71%		1.71%		1.65%
Line of Credit Facility [Line Items]
Maturity date			Dec. 31, 2032
Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Debt	351,523,000		351,523,000		348,195,000
Maturity date			Dec. 31, 2026
Weighted average interest rate (in hundredths)	8.48%		8.48%		8.61%
Line of Credit Facility [Line Items]
Maturity date			Dec. 31, 2026
Convertible Debt [Member]
Debt Instrument [Line Items]
Debt	246,518,000		246,518,000		241,897,000
Maturity date			Jun. 30, 2018
Weighted average interest rate (in hundredths)	2.75%		2.75%		2.75%
Unamortized debt discount	69,800,000		69,800,000
Principal	316,300,000		316,300,000
Line of Credit Facility [Line Items]
Maturity date			Jun. 30, 2018
Construction Financing [Member]
Debt Instrument [Line Items]
Debt	7,194,000		7,194,000		6,591,000
Maturity date			Dec. 31, 2024
Weighted average interest rate (in hundredths)	7.00%		7.00%		7.00%
Line of Credit Facility [Line Items]
Maturity date			Dec. 31, 2024
Notes Payable, Insurance Premiums Due 2013 [Member]
Debt Instrument [Line Items]
Debt	$ 9,001,000		$ 9,001,000		$ 2,545,000
Maturity date			Dec. 31, 2013
Weighted average interest rate (in hundredths)	2.68%		2.68%		3.11%
Line of Credit Facility [Line Items]
Maturity date			Dec. 31, 2013