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Financial Instruments and Fair Value Measurements (Estimated Fair Values of Financial Instruments) (Details) - USD ($)
$ in Thousands
Dec. 31, 2017
Sep. 30, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Notes receivable from municipalities, Carrying Cost $ 14,217 $ 14,507
Investments in short-term time deposits, Carrying Cost 9,219 8,223
Long-term debt, excluding current portion, Carrying Cost (585,059) (582,080)
Fair Value, Inputs, Level 2 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Notes receivable from municipalities, Estimated Fair Value 14,771 15,848
Investments in short-term time deposits, Estimated Fair Value 9,191 8,227
Long-term debt, excluding current portion, Estimated Fair Value $ (596,136) $ (592,317)