Fair Value Measurements (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Sep. 30, 2023
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	$ 343,174	$ 450,211
Derivative Asset, Statement of Financial Position		Prepaid expenses and other current assets
Liabilities, Fair Value Disclosure [Abstract]
Derivative Liability, Statement of Financial Position	Accrued expenses and other current liabilities
Fair Value, Recurring
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	$ 343,174	$ 450,211
Foreign exchange contracts	77	44
Net investment hedge		13,036
Total Assets	900,892	989,243
Liabilities, Fair Value Disclosure [Abstract]
Net investment hedge	4,993
Foreign exchange contracts	350	421
Total Liabilities	5,343	421
Fair Value, Recurring | Cash Equivalents
Assets, Fair Value Disclosure [Abstract]
Cash equivalents	557,641	525,952
Fair Value, Recurring | Fair Value, Inputs, Level 1
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	61,797	85,949
Total Assets	619,438	611,901
Fair Value, Recurring | Fair Value, Inputs, Level 1 | Cash Equivalents
Assets, Fair Value Disclosure [Abstract]
Cash equivalents	557,641	525,952
Fair Value, Recurring | Fair Value, Inputs, Level 2
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	281,377	364,262
Foreign exchange contracts	77	44
Net investment hedge		13,036
Total Assets	281,454	377,342
Liabilities, Fair Value Disclosure [Abstract]
Net investment hedge	4,993
Foreign exchange contracts	350	421
Total Liabilities	$ 5,343	$ 421