Investments - Summary of Fair Value of Investments Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Sep. 30, 2021
Assets
Short-term investments	$ 137,753	$ 149,057
Long-term investments	56,255	48,051
Convertible senior notes hedge	42,821	48,208
Total assets at fair value	236,829	245,316
Current liabilities:
Acquisition-related contingent consideration	11,210	11,050
Non-current liabilities:
Acquisition-related contingent consideration	5,590	5,720
Embedded conversion derivative	42,821	48,208
Total liabilities at fair value	59,621	64,978
U.S. Treasury
Assets
Short-term investments	7,700	4,223
Long-term investments	7,468	6,995
Asset-backed securities
Assets
Short-term investments	4,512	4,811
Corporate debt securities
Assets
Short-term investments	125,541	140,023
Long-term investments	45,900	38,148
Foreign government and agency securities
Assets
Long-term investments	2,887	2,908
Quoted Prices in Active Markets (Level 1)
Assets
Short-term investments	7,700	4,223
Long-term investments	7,468	6,995
Convertible senior notes hedge	0	0
Total assets at fair value	15,168	11,218
Current liabilities:
Acquisition-related contingent consideration	0	0
Non-current liabilities:
Acquisition-related contingent consideration	0	0
Embedded conversion derivative	0	0
Total liabilities at fair value	0	0
Quoted Prices in Active Markets (Level 1) \| U.S. Treasury
Assets
Short-term investments	7,700	4,223
Long-term investments	7,468	6,995
Quoted Prices in Active Markets (Level 1) \| Asset-backed securities
Assets
Short-term investments	0	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) \| Foreign government and agency securities
Assets
Long-term investments	0	0
Significant Other Observable Inputs (Level 2)
Assets
Short-term investments	130,053	144,834
Long-term investments	48,787	41,056
Convertible senior notes hedge	42,821	48,208
Total assets at fair value	221,661	234,098
Current liabilities:
Acquisition-related contingent consideration	0	0
Non-current liabilities:
Acquisition-related contingent consideration	0	0
Embedded conversion derivative	42,821	48,208
Total liabilities at fair value	42,821	48,208
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	4,512	4,811
Significant Other Observable Inputs (Level 2) \| Corporate debt securities
Assets
Short-term investments	125,541	140,023
Long-term investments	45,900	38,148
Significant Other Observable Inputs (Level 2) \| Foreign government and agency securities
Assets
Long-term investments	2,887	2,908
Significant Unobservable Inputs (Level 3)
Assets
Short-term investments	0	0
Long-term investments	0	0
Convertible senior notes hedge	0	0
Total assets at fair value	0	0
Current liabilities:
Acquisition-related contingent consideration	11,210	11,050
Non-current liabilities:
Acquisition-related contingent consideration	5,590	5,720
Embedded conversion derivative	0	0
Total liabilities at fair value	16,800	16,770
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
Significant Unobservable Inputs (Level 3) \| Corporate debt securities
Assets
Short-term investments	0	0
Long-term investments	0	0
Significant Unobservable Inputs (Level 3) \| Foreign government and agency securities
Assets
Long-term investments	$ 0	$ 0

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