Commitments And Contingencies (Narrative) (Details) ft² in Thousands	3 Months Ended	12 Months Ended			60 Months Ended
	Jan. 01, 2011	Sep. 30, 2017 USD ($) ft²	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2015
Commitments And Contingencies [Line Items]
Lease expense, net of sublease income		$ 35,800,000	$ 37,200,000	$ 36,900,000
Lease renewal term	10 years
Annual base rent plus operating expenses		7,400,000
Operating Lease Utilities Cost		$ 1,500,000
Additional term of lease renewal		10 years
Landlord reimbursements		$ 12,800,000
Boston Lease Square Feet | ft²		250
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		4,300,000	4,200,000
Bank guarantees outstanding collateralized		1,200,000	1,200,000
Accounts receivable, net of allowance for doubtful accounts of $1,062 and $1,012 at September 30, 2017 and 2016, respectively		152,299,000	161,357,000
Pending or Threatened Litigation [Member]
Commitments And Contingencies [Line Items]
Loss contingency accrual		300,000	$ 3,600,000
Korea
Commitments And Contingencies [Line Items]
Income Tax Examination, Description					12
Customer Contracts [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Accounts receivable, net of allowance for doubtful accounts of $1,062 and $1,012 at September 30, 2017 and 2016, respectively		17,300,000
Customer Contracts [Member] | Minimum [Member]
Commitments And Contingencies [Line Items]
Accounts receivable, net of allowance for doubtful accounts of $1,062 and $1,012 at September 30, 2017 and 2016, respectively		$ 0