Financial Instruments and Fair Value Measurements (Estimated Fair Values of Financial Instruments) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 30, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes receivable from municipalities, Carrying Cost	$ 12,020	$ 12,346
Investments in short-term time deposits, Carrying Cost	13,386	13,509
Long-term debt, Carrying Cost	(833,172)	(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	12,868	13,100
Investments in short-term time deposits, Estimated Fair Value	13,371	13,468
Long-term debt, Estimated Fair Value	$ (887,834)	$ (928,618)