FAIR VALUE OF FINANCIAL INSTRUMENTS (Details) (USD $)	Sep. 30, 2011	Sep. 30, 2010
Assets
Short-term investments	$ 25,829,000	$ 84,081,000
Debt instruments
Estimated fair value of long-term debt	17,500,000	21,600,000
Carrying value of long-term debt	15,918,000	20,494,000
Short-term investments -U.S. government agency | Assets and liabilities measured at fair value on a recurring basis | Level 2
Assets
Short-term investments		36,000,000
Short-term investments -U.S. government agency | Assets and liabilities measured at fair value on a recurring basis | Total
Assets
Short-term investments		36,000,000
Short-term investments - tax exempt bonds | Assets and liabilities measured at fair value on a recurring basis | Level 2
Assets
Short-term investments	25,829,000	48,081,000
Short-term investments - tax exempt bonds | Assets and liabilities measured at fair value on a recurring basis | Total
Assets
Short-term investments	25,829,000	48,081,000
Assets and liabilities measured at fair value on a recurring basis | Level 1
Assets
Cash equivalents	266,842,000	129,756,000
Total assets	266,842,000	129,756,000
Net Assets
Net assets	266,842,000	129,756,000
Assets and liabilities measured at fair value on a recurring basis | Level 2
Assets
Current derivative assets	7,466,000	11,428,000
Total assets	33,295,000	95,509,000
Liabilities
Current derivative liabilities	7,522,000	3,193,000
Noncurrent derivative liabilities	6,164,000	4,748,000
Net Assets
Net assets	19,609,000	87,568,000
Assets and liabilities measured at fair value on a recurring basis | Total
Assets
Cash equivalents	266,842,000	129,756,000
Current derivative assets	7,466,000	11,428,000
Total assets	300,137,000	225,265,000
Liabilities
Current derivative liabilities	7,522,000	3,193,000
Noncurrent derivative liabilities	6,164,000	4,748,000
Net Assets
Net assets	$ 286,451,000	$ 217,324,000