Revenue from Contracts with Customers - Additional Information (Details) - USD ($)	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Oct. 01, 2018
Revenue from External Customer [Line Items]
Contract with customer, asset, expected to be transferred to receivables within the next 12 months and therefore	$ 6,900,000
Contract with customer, asset, reclassified to receivable	15,100,000
Contract with customer, asset, decrease in contract assets	(9,000,000.0)
Contract with customer, asset, increase in contract assets related to revenue recognized	6,100,000
Deferred revenue, revenue recognized	379,800,000
Deferred revenue, additions	409,700,000
Short term and long term accounts receivable	$ 511,300,000	$ 412,500,000
Capitalized contract cost, amortization period	5 years
Amortization expense related to costs to obtain a contract with a customer	$ 36,200,000	30,400,000
Impairments of the contract cost asset	0	0
Deferred revenue	426,465,000	396,632,000
Revenue, remaining performance obligation, amount	1,220,900,000
Unrecorded
Revenue from External Customer [Line Items]
Revenue, remaining performance obligation, amount	794,400,000
Other Assets
Revenue from External Customer [Line Items]
Capitalized contract cost, net	72,900,000	64,800,000
Other Current Assets
Revenue from External Customer [Line Items]
Capitalized contract cost, net	$ 33,900,000	$ 27,700,000
Accumulated Deficit | Cumulative Effect, Period of Adoption, Adjustment
Revenue from External Customer [Line Items]
Cumulative effect of new accounting principle			$ 363,200,000
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201409Member
Accumulated Deficit | Revenue from Contract with Customer Benchmark | Cumulative Effect, Period of Adoption, Adjustment
Revenue from External Customer [Line Items]
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201409Member
Accumulated Deficit | Deferred Revenue | Revenue from Contract with Customer Benchmark | Cumulative Effect, Period of Adoption, Adjustment
Revenue from External Customer [Line Items]
Cumulative effect of new accounting principle			143,200,000
Accumulated Deficit | Other Assets | Revenue from Contract with Customer Benchmark | Cumulative Effect, Period of Adoption, Adjustment
Revenue from External Customer [Line Items]
Cumulative effect of new accounting principle			5,100,000
Accumulated Deficit | Unbilled Contracts Receivables | Revenue from Contract with Customer Benchmark | Cumulative Effect, Period of Adoption, Adjustment
Revenue from External Customer [Line Items]
Cumulative effect of new accounting principle			218,500,000
Accounting Standards Update 2014-09 | Accumulated Deficit
Revenue from External Customer [Line Items]
Cumulative effect of new accounting principle in period of adoption, related to offsetting current liability			2,800,000
Cumulative effect of new accounting principle in period of adoption, gross			432,200,000
Cumulative effect of new accounting principle in period of adoption, related to deferral of commission expenses			70,000,000.0
Accounting Standards Update 2014-09 | Accumulated Deficit | Revenue from Contract with Customer Benchmark | Cumulative Effect, Period of Adoption, Adjustment
Revenue from External Customer [Line Items]
Cumulative effect of new accounting principle			$ 366,800,000