SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2012 item	Dec. 31, 2011	Dec. 31, 2010
Developments
Land & improvements	$ 172,614,000	$ 150,273,000
Pre-development costs	78,198,000	34,686,000
Condominium rights	22,801,000	22,801,000
Total Developments	273,613,000	207,760,000
Investments in Real Estate Affiliates
Minimum period over which differences between carrying amount of equity method investment and share of underlying equity are amortized	5 years
Maximum period over which differences between carrying amount of equity method investment and share of underlying equity are amortized	45 years
Rental Revenue
Number of residential condominium projects located in Natick (Boston), Massachusetts	215
Percentage rent in lieu of fixed minimum rent	3,800,000	3,900,000	3,900,000
Straight-line rent receivables	6,900,000	7,600,000
Overage rent	$ 2,800,000	$ 3,000,000	$ 3,400,000
Minimum | Master Planned Communities
Useful lives of assets
Estimated useful lives	20 years
Maximum | Master Planned Communities
Useful lives of assets
Estimated useful lives	40 years
Buildings and improvements | Minimum
Useful lives of assets
Estimated useful lives	10 years
Buildings and improvements | Maximum
Useful lives of assets
Estimated useful lives	45 years
Equipment, tenant improvements and fixtures | Minimum
Useful lives of assets
Estimated useful lives	5 years
Equipment, tenant improvements and fixtures | Maximum
Useful lives of assets
Estimated useful lives	10 years
Computer hardware and software, and vehicles | Minimum
Useful lives of assets
Estimated useful lives	3 years
Computer hardware and software, and vehicles | Maximum
Useful lives of assets
Estimated useful lives	5 years