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Derivatives - Details of Derivatives Held to Manage Foreign Currency Risk (Detail) - USD ($) | Mar. 31, 2016 | Sep. 30, 2015
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Not Designated as Hedging Instrument [Member] | Forward Foreign Currency Contracts [Member] |  |  |
Derivative [Line Items] |  |  |
Notional amount, net of forward foreign currency contract no designation hedge derivatives | [1] | $ 3,000,000 | $ 2,000,000
[1] | Cabot’s forward foreign exchange contracts are denominated primarily in the British pound sterling, Czech koruna, and Indonesian rupiah.

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- Definition Aggregate notional amount specified by the derivative(s). Expressed as an absolute value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
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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. + References No definition available. + Details
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- Details
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- Details
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