Operations and summar of significant accounting policies (Schedule of Accounts Receivable) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Sep. 30, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for uncollectible customer amounts	$ (3,776)	$ (2,540)
Accounts receivable	402,182	343,768
Trade Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross	367,715	341,215
Accounts Receivable from Chinese Financial Institution [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross	$ 38,243	$ 5,093