Investments - Narrative (Details) - USD ($)	3 Months Ended		6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021	Sep. 30, 2021
Subsidiary, Sale of Stock [Line Items]
Equity securities without readily determinable fair value, upward price adjustment, cumulative amount	$ 13,800,000		$ 13,800,000		$ 5,100,000
Change in fair value of investments			133,100,000	$ (581,300,000)
Equity securities without readily determinable fair value, upward price adjustment, annual amount	8,700,000		8,700,000
Income (loss) from equity method investments	$ 7,400,000	$ 0	$ 14,200,000	0
PTC
Subsidiary, Sale of Stock [Line Items]
Number of shares purchased (in shares)	10,571,340		10,571,340		10,582,010
Change in fair value of investments	$ 142,000,000	$ (190,900,000)	$ 127,600,000	$ (581,300,000)