Fair Value Measurements (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Sep. 30, 2023
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	$ 611,238	$ 450,211
Derivative Asset, Statement of Financial Position	Prepaid expenses and other current assets	Prepaid expenses and other current assets
Fair Value, Recurring
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	$ 611,238	$ 450,211
Foreign exchange contracts	217	44
Net investment hedge	350	13,036
Total Assets	807,202	989,243
Liabilities, Fair Value Disclosure [Abstract]
Foreign exchange contracts	141	421
Total Liabilities	141	421
Fair Value, Recurring | Cash Equivalents
Assets, Fair Value Disclosure [Abstract]
Cash equivalents	195,397	525,952
Fair Value, Recurring | Fair Value, Inputs, Level 1
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	225,926	85,949
Total Assets	406,681	611,901
Fair Value, Recurring | Fair Value, Inputs, Level 1 | Cash Equivalents
Assets, Fair Value Disclosure [Abstract]
Cash equivalents	180,755	525,952
Fair Value, Recurring | Fair Value, Inputs, Level 2
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	385,312	364,262
Foreign exchange contracts	217	44
Net investment hedge	350	13,036
Total Assets	400,521	377,342
Liabilities, Fair Value Disclosure [Abstract]
Foreign exchange contracts	141	421
Total Liabilities	141	$ 421
Fair Value, Recurring | Fair Value, Inputs, Level 2 | Cash Equivalents
Assets, Fair Value Disclosure [Abstract]
Cash equivalents	$ 14,642