Commitments And Contingencies (Narrative) (Details) ft² in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2010	Sep. 30, 2018 USD ($) ft²	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)
Commitments And Contingencies [Line Items]
Lease expense, net of sublease income		$ 36,900,000	$ 35,800,000	$ 37,200,000
Lease renewal term	10 years
Additional term of lease renewal		10 years
Annual base rent plus operating expenses		$ 7,400,000
Operating Lease Utilities Cost		1,600,000
Landlord reimbursements		$ 12,800,000
Boston Lease Square Feet | ft²		250,000
Boston lease year one payments		$ 11,000,000
Boston lease per square foot annual increase		1
Boston lease annual increase		$ 300,000
Boston lease building operating cost percent		63.00%
Boston lease building operating cost amount estimate year one		$ 7,100,000
Boston lease leasehold improvement allowance		25,000,000
Boston lease leasehold improvement allowance per square foot		100
Letters of credit and bank guarantees outstanding		15,500,000	4,300,000
Bank guarantees outstanding collateralized		1,100,000	1,200,000
Allowance for Sales Credits		2,000,000
Pending or Threatened Litigation [Member]
Commitments And Contingencies [Line Items]
Loss contingency accrual		900,000	$ 300,000
Korea
Commitments And Contingencies [Line Items]
Income Tax Examination, Estimate of Possible Loss		12,000,000
Minimum [Member]
Commitments And Contingencies [Line Items]
Loss Contingency, Estimate of Possible Loss		700,000
Maximum [Member]
Commitments And Contingencies [Line Items]
Loss Contingency, Estimate of Possible Loss		5,000,000
Customer Contracts [Member]
Commitments And Contingencies [Line Items]
Net revenue write-down		9,300,000
Technology Services Revenue [Member] | Customer Contracts [Member]
Commitments And Contingencies [Line Items]
Net revenue write-down		14,500,000
License Revenue [Member] | Customer Contracts [Member]
Commitments And Contingencies [Line Items]
Net revenue write-down offset		$ 5,200,000