NOTES PAYABLE TO BANKS (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Line of Credit Facility [Line Items]
Weighted average interest rates (in hundredths)	1.61%	1.41%
Notes payable to banks	$ 76,160,000	$ 154,516,000
Average bank borrowings	85,113,000	124,697,000
Weighted average interest rates (including amortization of loan costs) (in hundredths)	2.01%	1.65%
Amortization of bank loan costs	342,000	300,000	314,000
Seven bank group unsecured revolving credit facility [Member]
Line of Credit Facility [Line Items]
Unsecured revolving credit facility available borrowings	200,000,000
Banks included in the unsecured revolving credit facility group	7
Line Of Credit Facility Commitment Fee Basis Points Minimum	0.15%
Line Of Credit Facility Commitment Fee Basis Points Maximum	0.20%
Interest rate on the facility, LIBOR basis spread on variable rate (in hundredths)	0.85%
Annual facility fee	0.20%
Weighted average interest rates (in hundredths)	1.065%
Notes payable to banks	71,000,000
Additional remaining line of credit	129,000,000
PNC N.A. unsecured revolving credit facility [Member]
Line of Credit Facility [Line Items]
Unsecured revolving credit facility available borrowings	25,000,000
Interest rate on the facility, LIBOR basis spread on variable rate (in hundredths)	1.65%
Weighted average interest rates (in hundredths)	1.859%
Notes payable to banks	5,160,000
Additional remaining line of credit	19,840,000
Subsequent Event [Member]
Line of Credit Facility [Line Items]
Unsecured revolving credit facility available borrowings	25,000,000
Interest rate on the facility, LIBOR basis spread on variable rate (in hundredths)	1.175%
Annual facility fee	0.225%
Weighted average interest rates (in hundredths)	1.377%
Unsecured revolving credit facility term (in years)	4
Extension option on credit facility	1 year
Subsequent Event [Member] | Nine bank group unsecured revolving credit facility [Member]
Line of Credit Facility [Line Items]
Unsecured revolving credit facility available borrowings	225,000,000
Banks included in the unsecured revolving credit facility group	9
Interest rate on the facility, LIBOR basis spread on variable rate (in hundredths)	1.175%
Annual facility fee	0.225%
Weighted average interest rates (in hundredths)	1.385%
Unsecured revolving credit facility term (in years)	4
Extension option on credit facility	1 year
Line of Credit Facility, Additional Borrowing Capacity	$ 100,000,000