Revenue from Contracts with Customers - Additional Information (Details) - USD ($)	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 28, 2020	Mar. 31, 2021	Mar. 28, 2020	Sep. 30, 2020
Revenue from External Customer [Line Items]
Contract with customer, asset, expected to be transferred to receivables within the next 12 months and therefore	$ 7,600,000		$ 7,600,000
Contract with customer, asset, reclassified to receivable			6,300,000
Contract with customer, asset, increase in contract assets related to revenue recognized			4,600,000
Impairments of the contract cost asset	0	$ 0	0	$ 0
Deferred revenue, revenue recognized			302,900,000
Deferred revenue, additions			353,300,000
Short term and long term accounts receivable	578,100,000		578,100,000		$ 511,300,000
Refund liability	39,600,000		39,600,000		34,500,000
Allowance for doubtful accounts receivable	500,000		500,000		500,000
Amortization expense related to costs to obtain a contract with a customer	11,000,000.0	$ 8,500,000	21,400,000	$ 16,200,000
Deferred revenue	492,421,000		492,421,000		426,465,000
Revenue, remaining performance obligation, amount	1,386,900,000		1,386,900,000
Unrecorded
Revenue from External Customer [Line Items]
Revenue, remaining performance obligation, amount	894,500,000		894,500,000
Other Current Assets
Revenue from External Customer [Line Items]
Capitalized contract cost, net	41,000,000.0		41,000,000.0		33,900,000
Other Assets
Revenue from External Customer [Line Items]
Capitalized contract cost, net	$ 73,400,000		73,400,000		$ 72,900,000
Arena Solutions
Revenue from External Customer [Line Items]
Deferred revenue increased			$ 15,500,000