Financial Instruments and Fair Value Measurements (Estimated Fair Values of Financial Instruments) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Sep. 30, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes receivable from municipalities, Carrying Cost	$ 12,130	$ 12,346
Investments in short-term time deposits, Carrying Cost	88	13,509
Long-term debt, Carrying Cost	973,165	867,377
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes receivable from municipalities, Estimated Fair Value	13,100	13,100
Investments in short-term time deposits, Estimated Fair Value	90	13,468
Long-term debt, Estimated Fair Value	$ 1,016,377	$ 928,618