Financial Instruments and Fair Value Measurements (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Financial liability on recurring basis	$ 0
Investments in Short-Term Time Deposits [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Interest rate used to estimate fair value	5.60%	5.30%
Long Term Notes Receivable From Municipalities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Interest rate used to estimate fair value	2.50%	2.60%
Long-Term Debt [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Interest rate used to estimate fair value	2.30%	2.40%