Derivative Financial Instruments - Summary of Outstanding Forward Foreign Currency Contracts by Currency (Detail) € in Thousands, £ in Thousands, $ in Thousands, $ in Thousands	Mar. 31, 2021 EUR (€)	Mar. 31, 2021 USD ($)	Mar. 31, 2021 GBP (£)	Mar. 31, 2021 SGD ($)	Sep. 30, 2020 EUR (€)	Sep. 30, 2020 USD ($)	Sep. 30, 2020 GBP (£)	Sep. 30, 2020 SGD ($)
Foreign Exchange Contracts To Sell European Euro for US Dollar
Derivative [Line Items]
Fair value of forward foreign currency contracts to sell and buy foreign currency		$ 0				$ 0
Foreign Exchange Contracts To Sell European Euro for US Dollar | Foreign currency forward contracts | Short | Not Designated as Hedging Instrument
Derivative [Line Items]
Contract amount of forward foreign currency contracts	€ 19,200	22,643			€ 15,000	17,656
Foreign Exchange Contracts To Purchase British Pounds With US Dollars
Derivative [Line Items]
Fair value of forward foreign currency contracts to sell and buy foreign currency		0				0
Foreign Exchange Contracts To Purchase British Pounds With US Dollars | Foreign currency forward contracts | Short | Not Designated as Hedging Instrument
Derivative [Line Items]
Contract amount of forward foreign currency contracts		20,400	£ 14,780			21,300	£ 16,555
Foreign Exchange Contracts To Purchase Singapore Dollars With US Dollars
Derivative [Line Items]
Fair value of forward foreign currency contracts to sell and buy foreign currency		0				0
Foreign Exchange Contracts To Purchase Singapore Dollars With US Dollars | Foreign currency forward contracts | Short | Not Designated as Hedging Instrument
Derivative [Line Items]
Contract amount of forward foreign currency contracts		$ 4,300		$ 5,790		$ 5,700		$ 7,815