Summary of Significant Accounting Policies (Narrative) (Details) - USD ($) shares in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017	Oct. 01, 2019	Oct. 01, 2018	Sep. 30, 2016
Summary Of Significant Accounting Policies [Line Items]
Contract with customer, refund liability	$ 22,900,000
Cost method investments	9,400,000	$ 1,700,000
Proceeds From Sale Of Cost Method Investments		13,700,000
Gain on sale of cost-method investments		3,700,000
Allowance for doubtful accounts receivable	700,000	600,000	$ 1,100,000			$ 1,000,000.0
Allowance for credit loss, writeoff	200,000	1,000,000.0	1,500,000
Bad debt expense including general and administrative expense	300,000	500,000	1,500,000
Development costs for software	0	0	0
Capitalized software in connection with acquisition		800,000
Advertising expense	3,600,000	2,900,000	2,500,000
Cumulative translation adjustment gains (loss)	91,200,000	66,400,000
Pension benefits, before tax	(34,900,000)	27,000,000.0
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax	(24,800,000)	19,200,000
AOCI, Debt Securities, Available-for-sale, Adjustment, after Tax	100,000	(400,000)
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Before Tax		(400,000)
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax		(400,000)
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Net Investment Hedges, Before Tax	(6,800,000)
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Net Investment Hedges, Effect Net of Tax	$ (5,100,000)
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	1.0
Deferred Tax Assets, Other	$ 1,623,000	1,152,000
Total stockholders’ equity	1,201,998,000	874,589,000	885,436,000			842,666,000
Deferred tax assets	198,634,000	165,566,000
Other income (expense), net	$ 305,000	(2,284,000)	(772,000)
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Percent of standalone selling price for subscriptions that contains license	50.00%
Percent of standalone selling price for subscriptions that contains support	45.00%
Minimum [Member] | Computer Hardware And Software [Member]
Summary Of Significant Accounting Policies [Line Items]
Amortization period (in years)	3 years
Minimum [Member] | Furniture And Fixtures [Member]
Summary Of Significant Accounting Policies [Line Items]
Amortization period (in years)	3 years
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Percent of standalone selling price for subscriptions that contains license	55.00%
Percent of standalone selling price for subscriptions that contains support	50.00%
Maximum [Member] | Purchased Software [Member]
Summary Of Significant Accounting Policies [Line Items]
Amortization period (in years)	11 years
Maximum [Member] | Customer Lists [Member]
Summary Of Significant Accounting Policies [Line Items]
Amortization period (in years)	12 years
Maximum [Member] | Trademarks And Trade Names [Member]
Summary Of Significant Accounting Policies [Line Items]
Amortization period (in years)	12 years
Maximum [Member] | Computer Hardware And Software [Member]
Summary Of Significant Accounting Policies [Line Items]
Amortization period (in years)	5 years
Maximum [Member] | Furniture And Fixtures [Member]
Summary Of Significant Accounting Policies [Line Items]
Amortization period (in years)	8 years
Not Designated as Hedging Instrument [Member] | Foreign Exchange Forward [Member]
Summary Of Significant Accounting Policies [Line Items]
Derivative maturity	3 months
Accounting Standards Update 2016-16 [Member]
Summary Of Significant Accounting Policies [Line Items]
Deferred tax assets					$ 75,300,000
Other Tax Assets					6,000,000.0
Other Tax Liabilities					3,000,000.0
Accounting Standards Update 2017-07 [Member]
Summary Of Significant Accounting Policies [Line Items]
Other income (expense), net		600,000	900,000
Accounting Standards Update 2016-02 [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Operating Lease, Liability				$ 233,000,000
Operating Lease, Right-of-Use Asset				162,000,000
Accounting Standards Update 2016-02 [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Operating Lease, Liability				238,000,000
Operating Lease, Right-of-Use Asset				$ 167,000,000
Accumulated Deficit [Member]
Summary Of Significant Accounting Policies [Line Items]
Total stockholders’ equity	$ (191,390,000)	(599,409,000)	$ (650,840,000)			$ (657,079,000)
Accumulated Deficit [Member] | Accounting Standards Update 2016-16 [Member]
Summary Of Significant Accounting Policies [Line Items]
Total stockholders’ equity					$ 72,300,000
Net Investment Hedging [Member] | Designated as Hedging Instrument [Member] | Foreign Exchange Forward [Member]
Summary Of Significant Accounting Policies [Line Items]
Derivative maturity	3 months
Derivative, remaining maturity	3 months
Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member] | Foreign Exchange Forward [Member]
Summary Of Significant Accounting Policies [Line Items]
Derivative, remaining maturity	15 months
Other Current Assets [Member]
Summary Of Significant Accounting Policies [Line Items]
Restricted Cash	$ 1,100,000	$ 1,100,000