Debt (Details) (USD $)			6 Months Ended				1 Months Ended			1 Months Ended		6 Months Ended				6 Months Ended		6 Months Ended	12 Months Ended	6 Months Ended		12 Months Ended		6 Months Ended		6 Months Ended		6 Months Ended		6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 First mortgage loan issued on April 3, 2013 [Member]	Jun. 30, 2013 First mortgage loan issued on April 12, 2013 [Member]	Jun. 30, 2013 First mortgage loan issued on April 22, 2013 [Member]	Jun. 30, 2013 First mortgage loan issued on May 30, 2013 [Member]	Aug. 01, 2013 First mortgage loan issued on August 1, 2013 [Member]	Aug. 01, 2013 First mortgage loan issued on August 1, 2013 [Member] Minimum [Member]	Aug. 01, 2013 First mortgage loan issued on August 1, 2013 [Member] Maximum [Member]	Aug. 01, 2013 Loans maturing in August 2020 [Member]	Aug. 01, 2013 Loans maturing in August 2023 [Member]	Jun. 30, 2013 Line of Credit [Member]	Dec. 31, 2012 Line of Credit [Member]	Jun. 30, 2013 Line of Credit [Member] Maximum [Member]	Jun. 30, 2013 Secured and unsecured letter of credit facilities	Jun. 30, 2013 Mortgage Notes Payable [Member]	Dec. 31, 2012 Mortgage Notes Payable [Member]	Jun. 30, 2013 $150 Million Series A Notes Payable [Member]	Dec. 31, 2012 $150 Million Series A Notes Payable [Member]	Jun. 30, 2013 Discount Mortgage Note payable due June 2013 [Member]	Dec. 31, 2012 Discount Mortgage Note payable due June 2013 [Member]	Dec. 31, 2012 Variable rate tax exempt bonds [Member]	Jun. 30, 2013 Variable rate tax exempt bonds [Member]	Jun. 30, 2013 Capital Lease Obligations [Member]	Dec. 31, 2012 Capital Lease Obligations [Member]	Jun. 30, 2013 Convertible Debt [Member]	Dec. 31, 2012 Convertible Debt [Member]	Jun. 30, 2013 Construction Financing [Member]	Dec. 31, 2012 Construction Financing [Member]	Jun. 30, 2013 Notes Payable, Insurance Premiums Due 2013 [Member]	Dec. 31, 2012 Notes Payable, Insurance Premiums Due 2013 [Member]
Long-Term Debt, Capital Leases and Financing Obligations [Line Items]
Debt	$ 2,555,949,000	$ 2,599,369,000														$ 1,832,236,000	$ 1,701,515,000	$ 142,240,000	$ 144,384,000	$ 0	$ 80,533,000	$ 99,847,000	$ 0	$ 306,382,000	$ 319,745,000	$ 256,284,000	$ 251,312,000	$ 6,499,000	$ 1,280,000	$ 12,308,000	$ 753,000
Less current portion	69,727,000	509,543,000
Long-term debt	2,486,222,000	2,089,826,000
Principal										75,000,000	97,100,000							150,000,000	150,000,000							316,300,000	316,300,000
Unamortized debt discount																200,000					1,000,000					60,000,000	65,000,000
Maturity date			Apr. 30, 2018	May 31, 2023	Apr. 30, 2018					Aug. 31, 2020	Aug. 31, 2023	Mar. 31, 2018						Aug. 31, 2013		Jun. 30, 2013		Dec. 31, 2032		Dec. 31, 2026		Jun. 30, 2018				Dec. 31, 2014
Maturity date, start																Dec. 31, 2014												Dec. 31, 2017
Maturity date, end																Dec. 31, 2023												Dec. 31, 2024
Number of communities securing debt (in number of communities)			1	23	2	8	4											5
Amount of cash collateral securing debt																		3,000,000
Weighted average interest rate																4.22%	4.62%				2.56%	1.65%		8.15%	8.16%	2.75%	2.75%	8.00%	8.00%	2.66%	2.81%
Description of variable rate basis			variable rate equal to 30-day LIBOR plus a margin of 275 basis points	variable rate equal to 30-day LIBOR plus a margin of 246 basis points	variable rate equal to 30-day LIBOR plus a margin of 275 basis points	variable rate equal to 30-day LIBOR plus a margin of 289 basis points	variable rate equal to 30-day LIBOR plus a margin ranging from 226 to 288 basis points											LIBOR plus 0.88%	LIBOR plus 0.88%
Basis spread on variable rate basis			2.75%	2.46%	2.75%	2.89%		2.26%	2.88%									0.88%	0.88%
Credit Facilities [Line Items]
Credit facility borrowing capacity												250,000,000	230,000,000	350,000,000	92,500,000
Maturity date			Apr. 30, 2018	May 31, 2023	Apr. 30, 2018					Aug. 31, 2020	Aug. 31, 2023	Mar. 31, 2018						Aug. 31, 2013		Jun. 30, 2013		Dec. 31, 2032		Dec. 31, 2026		Jun. 30, 2018				Dec. 31, 2014
Description of applicable margin calculation based on utilization percentage												Amounts drawn under the facility bear interest at 90-day LIBOR plus an applicable margin. The applicable margin varies with the percentage of the total commitment drawn, with a 3.25% margin at 25% or lower utilization, a 3.75% margin at utilization greater than 25% but less than or equal to 50%, and a 4.25% margin at greater than 50% utilization. For purposes of determining the interest rate, in no event will LIBOR be less than 0.5% per annum. The Company is also required to pay a quarterly commitment fee of 0.5% per annum on the unused portion of the facility.
Quarterly commitment fee												0.50%
Line of credit availability												225,300,000
Credit facility borrowings outstanding												70,000,000			75,000,000
Financings [Line Items]
Proceeds from debt financing			25,000,000	259,000,000	28,000,000	84,100,000	172,100,000
Repayment of debt			29,000,000	275,200,000	35,100,000	100,900,000	142,000,000
Principal										$ 75,000,000	$ 97,100,000							$ 150,000,000	$ 150,000,000							$ 316,300,000	$ 316,300,000
Description of Variable Rate Basis			variable rate equal to 30-day LIBOR plus a margin of 275 basis points	variable rate equal to 30-day LIBOR plus a margin of 246 basis points	variable rate equal to 30-day LIBOR plus a margin of 275 basis points	variable rate equal to 30-day LIBOR plus a margin of 289 basis points	variable rate equal to 30-day LIBOR plus a margin ranging from 226 to 288 basis points											LIBOR plus 0.88%	LIBOR plus 0.88%
Basis Spread on Variable Rate			2.75%	2.46%	2.75%	2.89%		2.26%	2.88%									0.88%	0.88%
Derivative, Remaining Maturity				5 years		5 years
Derivative, Cap Interest Rate				5.03%		4.68%
Maturity date			Apr. 30, 2018	May 31, 2023	Apr. 30, 2018					Aug. 31, 2020	Aug. 31, 2023	Mar. 31, 2018						Aug. 31, 2013		Jun. 30, 2013		Dec. 31, 2032		Dec. 31, 2026		Jun. 30, 2018				Dec. 31, 2014
Amortization period				30			30
Number of communities securing mortgage notes			1	23	2	8	4											5