UNSECURED BANK CREDIT FACILITIES (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Line of Credit Facility [Line Items]
Weighted average interest rates (in hundredths)	1.92%	1.87%
Weighted average interest rate (including amortization of loan costs)	2.35%	2.23%
Notes payable to banks	$ 99,401,000	$ 88,952,000
Average bank borrowings	96,162,000	112,971,000
Amortization of bank loan costs	413,000	410,000	342,000
Nine bank group unsecured revolving credit facility [Member]
Line of Credit Facility [Line Items]
Unsecured revolving credit facility available borrowings	225,000,000
Unsecured revolving credit facility maturity date	January 2017
Debt instrument, spread above LIBOR variable rate (in basis points)	117.5
Line of credit, facility fee (in basis points)	22.5
Banks included in the unsecured revolving credit facility group	9
Line of Credit Facility, Interest Rate at Period End	1.334%
Notes payable to banks	90,000,000
Extension option on credit facility	1 year
Expansion option on credit facility	100,000,000
Line of Credit Facility, Additional Borrowing Capacity	135,000,000
PNC N.A. unsecured revolving credit facility [Member]
Line of Credit Facility [Line Items]
Unsecured revolving credit facility available borrowings	25,000,000
Unsecured revolving credit facility maturity date	January 2017
Debt instrument, spread above LIBOR variable rate (in basis points)	117.5
Line of credit, facility fee (in basis points)	22.5
Line of Credit Facility, Interest Rate at Period End	1.346%
Notes payable to banks	9,401,000
Additional remaining line of credit	$ 15,599,000
Extension option on credit facility	1 year