Financial Instruments and Fair Value Measurements (Estimated Fair Values of Financial Instruments) (Details) - Level 2 [Member] - USD ($) $ in Thousands	Dec. 31, 2023	Sep. 30, 2023
ASSETS
Investments in short-term time deposits, Estimated Fair Value	$ 6,099	$ 6,095
Liabilities:
Long-term debt, Estimated Fair Value	619,230	661,507
Investments in short-term time deposits, Carrying Cost	6,101	6,107
Long-term debt, Carrying Cost	654,876	722,671
Long Term Notes Receivable from Municipalities [Member]
ASSETS
Notes receivable, Estimated Fair Value	7,861	7,794
Liabilities:
Notes receivable, Carrying Cost	$ 7,333	$ 7,688