FAIR VALUE OF FINANCIAL INSTRUMENTS (Details 3) (USD $)	Jun. 30, 2012	Dec. 31, 2011
Financial instruments that are not measured at fair value on a recurring basis
Variable-rate debt that has been swapped to a fixed rate	$ 172,000,000
Carrying Amount
Financial instruments that are not measured at fair value on a recurring basis
Fixed-rate debt	142,624,000	83,164,000
Variable-rate debt	465,046,000	468,100,000
SID bonds	51,727,000	55,213,000
Total	659,397,000	606,477,000
Estimated Fair Value
Financial instruments that are not measured at fair value on a recurring basis
Fixed-rate debt	144,098,000	85,047,000
Variable-rate debt	465,046,000	468,100,000
SID bonds	51,727,000	55,213,000
Total	$ 660,871,000	$ 608,360,000