Investments - Summary of Fair Value of Investments Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Sep. 30, 2020
Assets
Short-term investments	$ 138,302	$ 40,035
Long-term investments	36,643	1,963
Convertible senior notes hedge	54,334
Total assets at fair value	229,279	41,998
Current liabilities:
Acquisition-related contingent consideration	9,950	753
Liabilities, Noncurrent [Abstract]
Acquisition-related consideration, noncurrent	5,330
Embedded conversion derivative	54,334
Total liabilities at fair value	69,614	753
U.S. Treasury
Assets
Short-term investments	5,241	10,283
Long-term investments	4,997	0
Asset-backed securities
Assets
Short-term investments	6,052	4,759
Long-term investments	0
Corporate debt securities
Assets
Short-term investments	61,394	9,619
Long-term investments	28,727	1,963
Commercial paper
Assets
Short-term investments	65,615	15,374
Foreign government and agency securities
Assets
Long-term investments	2,919
Quoted Prices in Active Markets (Level 1)
Assets
Short-term investments	5,241	10,283
Long-term investments	4,997	0
Convertible senior notes hedge	0
Total assets at fair value	10,238	10,283
Current liabilities:
Acquisition-related contingent consideration	0	0
Liabilities, Noncurrent [Abstract]
Acquisition-related consideration, noncurrent	0
Embedded conversion derivative	0
Total liabilities at fair value	0	0
Quoted Prices in Active Markets (Level 1) \| U.S. Treasury
Assets
Short-term investments	5,241	10,283
Long-term investments	4,997	0
Quoted Prices in Active Markets (Level 1) \| Asset-backed securities
Assets
Short-term investments	0	0
Long-term investments	0
Quoted Prices in Active Markets (Level 1) \| Corporate debt securities
Assets
Short-term investments	0	0
Long-term investments	0	0
Quoted Prices in Active Markets (Level 1) \| Commercial paper
Assets
Short-term investments	0	0
Quoted Prices in Active Markets (Level 1) \| Foreign government and agency securities
Assets
Long-term investments	0
Significant Other Observable Inputs (Level 2)
Assets
Short-term investments	133,061	29,752
Long-term investments	31,646	1,963
Convertible senior notes hedge	54,334
Total assets at fair value	219,041	31,715
Current liabilities:
Acquisition-related contingent consideration	0	0
Liabilities, Noncurrent [Abstract]
Acquisition-related consideration, noncurrent	0
Embedded conversion derivative	54,334
Total liabilities at fair value	54,334	0
Significant Other Observable Inputs (Level 2) \| U.S. Treasury
Assets
Short-term investments	0	0
Long-term investments	0	0
Significant Other Observable Inputs (Level 2) \| Asset-backed securities
Assets
Short-term investments	6,052	4,759
Long-term investments	0
Significant Other Observable Inputs (Level 2) \| Corporate debt securities
Assets
Short-term investments	61,394	9,619
Long-term investments	28,727	1,963
Significant Other Observable Inputs (Level 2) \| Commercial paper
Assets
Short-term investments	65,615	15,374
Significant Other Observable Inputs (Level 2) \| Foreign government and agency securities
Assets
Long-term investments	2,919
Significant Unobservable Inputs (Level 3)
Assets
Short-term investments	0	0
Long-term investments	0	0
Convertible senior notes hedge	0
Total assets at fair value	0	0
Current liabilities:
Acquisition-related contingent consideration	9,950	753
Liabilities, Noncurrent [Abstract]
Acquisition-related consideration, noncurrent	5,330
Embedded conversion derivative	0
Total liabilities at fair value	15,280	753
Significant Unobservable Inputs (Level 3) \| U.S. Treasury
Assets
Short-term investments	0	0
Long-term investments	0	0
Significant Unobservable Inputs (Level 3) \| Asset-backed securities
Assets
Short-term investments	0	0
Long-term investments	0
Significant Unobservable Inputs (Level 3) \| Corporate debt securities
Assets
Short-term investments	0	0
Long-term investments	0	0
Significant Unobservable Inputs (Level 3) \| Commercial paper
Assets
Short-term investments	0	$ 0
Significant Unobservable Inputs (Level 3) \| Foreign government and agency securities
Assets
Long-term investments	$ 0

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