Employee benefit plans and deferred compensation - Narrative (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Sep. 30, 2018 |
Sep. 30, 2017 |
Sep. 30, 2016 |
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| Retirement Benefits [Abstract] | |||
| Employer contribution to 401(k) plans | $ 7.4 | $ 7.0 | $ 6.0 |
| Percentage of liabilities that can be met plan assets | 95.00% | ||
| Investments in mutual funds within the rabbi trust | $ 20.3 | ||
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- Definition Deferred Compensation Plan, Funded Percentage No definition available.
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- References No definition available.
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- Definition Amount of cost for defined contribution plan. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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