Financial Instruments and Fair Value Measurements (Narrative) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Financial liability on recurring basis	$ 23,000
Investments in Short-Term Time Deposits [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Interest rate used to estimate fair value	6.30%	5.30%
Long Term Notes Receivable From Municipalities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Interest rate used to estimate fair value	3.10%	2.60%
Long-Term Debt [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Interest rate used to estimate fair value	3.50%	2.40%
Cash [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	$ 59,838	$ 79,822
Investments in Reverse Repurchase Agreements [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	4,582	1
Investments in Term Deposits with Foreign Banks [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	19,174	$ 7,729
Restricted Investments in Term Deposits with Foreign Banks [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	$ 3,635