Geographical Information (Narrative) (Details)	3 Months Ended		6 Months Ended
	Mar. 31, 2019 customers	Mar. 31, 2018 customers	Mar. 31, 2019 segment customers	Mar. 31, 2018 customers	Sep. 30, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of reporting segments | segment			1
Concentration risk, customers | customers	4	3	4	2
Percentage of long-lived assets located in the United States	72.00%		72.00%		49.00%
Customer Concentration Risk | Sales Revenue, Segment
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Concentration risk percentage	67.00%	65.00%	71.00%	59.00%