Concentrations of credit risk and major customers - Schedule of Concentration of Risk, by Risk Factor (Details) - Total Revenue |
12 Months Ended | ||
|---|---|---|---|
Sep. 30, 2017 |
Sep. 30, 2016 |
Sep. 30, 2015 |
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| U.S. Federal Government | |||
| Concentration Risk [Line Items] | |||
| Revenue from major customers (as a percent) | 19.00% | 22.00% | 20.00% |
| New York | |||
| Concentration Risk [Line Items] | |||
| Revenue from major customers (as a percent) | 15.00% | 12.00% | 10.00% |
| United Kingdom | |||
| Concentration Risk [Line Items] | |||
| Revenue from major customers (as a percent) | 12.00% | 16.00% | |
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available.
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- Definition For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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