Investments - Summary of Fair Value of Investments Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Sep. 30, 2021
Assets:
Short-term investments:	$ 37,910	$ 149,057
Long-term investments:	31,493	48,051
Convertible senior notes hedge		48,208
Total assets at fair value	69,403	245,316
Current liabilities:
Acquisition-related contingent consideration	10,790	11,050
Non-current liabilities:
Acquisition-related contingent consideration	5,200	5,720
Embedded conversion derivative		48,208
Total liabilities at fair value	15,990	64,978
U.S. Treasury
Assets:
Short-term investments:	1,980	4,223
Long-term investments:	7,266	6,995
Asset-backed securities
Assets:
Short-term investments:		4,811
Corporate debt securities
Assets:
Short-term investments:	33,080	140,023
Long-term investments:	24,227	38,148
Foreign government and agency securities
Assets:
Short-term investments:	2,850
Long-term investments:		2,908
Quoted Prices in Active Markets (Level 1)
Assets:
Short-term investments:	1,980	4,223
Long-term investments:	7,266	6,995
Convertible senior notes hedge		0
Total assets at fair value	9,246	11,218
Current liabilities:
Acquisition-related contingent consideration	0	0
Non-current liabilities:
Acquisition-related contingent consideration	0	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:	1,980	4,223
Long-term investments:	7,266	6,995
Quoted Prices in Active Markets (Level 1) | Asset-backed securities
Assets:
Short-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) | Foreign government and agency securities
Assets:
Short-term investments:	0
Long-term investments:		0
Significant Other Observable Inputs (Level 2)
Assets:
Short-term investments:	35,930	144,834
Long-term investments:	24,227	41,056
Convertible senior notes hedge		48,208
Total assets at fair value	60,157	234,098
Current liabilities:
Acquisition-related contingent consideration	0	0
Non-current liabilities:
Acquisition-related contingent consideration	0	0
Embedded conversion derivative		48,208
Total liabilities at fair value	0	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:		4,811
Significant Other Observable Inputs (Level 2) | Corporate debt securities
Assets:
Short-term investments:	33,080	140,023
Long-term investments:	24,227	38,148
Significant Other Observable Inputs (Level 2) | Foreign government and agency securities
Assets:
Short-term investments:	2,850
Long-term investments:		2,908
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	10,790	11,050
Non-current liabilities:
Acquisition-related contingent consideration	5,200	5,720
Embedded conversion derivative		0
Total liabilities at fair value	15,990	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
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:
Short-term investments:	$ 0
Long-term investments:		$ 0