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Summary of significant accounting policies (Details 1)
12 Months Ended
Sep. 30, 2018
Machinery and equipment  
Accounting Policies [Line Items]  
Estimated useful lives 5 - 10 years
Transportation equipment  
Accounting Policies [Line Items]  
Estimated useful lives 4 years
Office equipment  
Accounting Policies [Line Items]  
Estimated useful lives 3 - 5 years
Leasehold improvement  
Accounting Policies [Line Items]  
Estimated useful lives Shorter of lease term or useful life