Derivatives - Details of Derivatives Held to Manage Foreign Currency Risk (Detail)		Dec. 31, 2021 USD ($)	Dec. 31, 2021 EUR (€)	Sep. 30, 2021 USD ($)	Sep. 30, 2021 EUR (€)
Net Investment Hedge [Member] | Cross Currency Swaps [Member]
Derivative [Line Items]
Notional Amount		$ 250,000,000
Net Investment Hedge [Member] | 3.4% Notes [Member] | Cross Currency Swaps [Member]
Derivative [Line Items]
Notional Amount		$ 250,000,000	€ 223,000,000	$ 250,000,000	€ 223,000,000
Net Investment Hedge [Member] | 3.4% Notes [Member] | Fixed Rate Debt [Member] | Cross Currency Swaps [Member]
Derivative [Line Items]
Interest rate on borrowing		3.40%	3.40%	3.40%	3.40%
Not Designated as Hedging Instrument [Member] | Forward Foreign Currency Contracts [Member]
Derivative [Line Items]
Notional Amount	[1]	$ 36,000,000		$ 48,000,000

[1] As of both December 31, 2021 and September 30, 2021, Cabot’s forward foreign exchange contracts were denominated in Indonesian rupiah and Czech koruna and the fair value of these derivative instruments were a nominal amount.