Operations and summary of significant accounting policies (Schedule of Accounts Receivable) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for uncollectible customer amounts	$ (3,938)	$ (3,776)
Accounts receivable	431,820	402,182
Trade Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross	412,567	367,715
Accounts Receivable from Chinese Financial Institution [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross	$ 23,191	$ 38,243