Summary of Significant Accounting Policies (Narrative) (Details)		3 Months Ended		9 Months Ended
	Oct. 31, 2018 USD ($) shares	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($) shares	Jun. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2019 USD ($) shares	Jun. 30, 2019 USD ($) $ / shares	Jun. 30, 2019 USD ($) segment	Jun. 30, 2018 USD ($) shares	Sep. 30, 2018 USD ($)	Oct. 25, 2017 USD ($)	Sep. 30, 2017 USD ($)
Schedule Of Summary Of Significant Accounting Policies [Line Items]
Cash and Cash Equivalents, at Carrying Value		$ 688,350,000	$ 599,268,000	$ 688,350,000	$ 688,350,000	$ 688,350,000	$ 688,350,000	$ 688,350,000	$ 688,350,000	$ 599,268,000	$ 424,707,000
Revenue Recognition
Number of reportable segments					1				1
Stock-Based Compensation
Share-based compensation expense		41,000,000.0	$ 38,700,000			119,200,000				$ 121,000,000.0
Unrecognized stock-based compensation cost		176,100,000		$ 176,100,000	$ 176,100,000	176,100,000	$ 176,100,000	$ 176,100,000	$ 176,100,000
Unrecognized stock-based compensation cost, period for recognition				2 years
Common Stock Repurchase
Stock Repurchased and Retired During Period, Shares | shares			903,000				1,185,881			3,211,000
Treasury Stock Acquired, Average Cost Per Share | $ / shares								$ 169.53
Stock Repurchase Program, Remaining Authorized Repurchase Amount		1,400,000,000		$ 1,400,000,000	1,400,000,000	1,400,000,000	$ 1,400,000,000	$ 1,400,000,000	1,400,000,000
Restricted Cash		3,013,000	$ 1,182,000	3,013,000	3,013,000	3,013,000	3,013,000	3,013,000	3,013,000	$ 1,182,000
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents		$ 691,363,000	$ 600,450,000	$ 691,363,000	$ 691,363,000	$ 691,363,000	$ 691,363,000	$ 691,363,000	$ 691,363,000	$ 600,450,000	$ 425,894,000		$ 674,452,000
Restricted Stock Units (RSUs) [Member]
Stock-Based Compensation
Approved RSUs to employees and executive officers pursuant to the Company's annual equity awards program | shares	774,313
Minimum [Member]
Revenue Recognition
Domestic accounts receivable terms of payment				30 days
International accounts receivable terms of payment				30 days
Finite-Lived Intangible Asset, Useful Life				2 years
Maximum [Member]
Revenue Recognition
Domestic accounts receivable terms of payment				45 days
International accounts receivable terms of payment				120 days
Finite-Lived Intangible Asset, Useful Life				15 years
October Twenty Six Two Thousand Ten Program [Member]
Common Stock Repurchase
Stock Repurchase Program, Authorized Amount	$ 1,000,000,000.0											$ 4,400,000,000
Annual Equity Program [Member] | Restricted Stock Units (RSUs) [Member]
Stock-Based Compensation
Percentage of the aggregate number of RSUs granted that vest in equal quarterly increments					50.00%
Portion of RSU grant subject to Company achieving specified quarterly revenue and EBITDA goals					50.00%
Percentage of quarterly performance stock grant based on achieving quarterly revenue goal					70.00%
Percentage of quarterly revenue goal to be achieved for performance stock grant					80.00%
Percentage of quarterly performance stock grant based on achieving EBITDA goal					30.00%
Percentage Of Quarterly Ebitda Goal To Be Achieved For Performance Stock Grant					80.00%
Threshold percentage of targeted goals above which quarterly performance stock grant is paid linearly					80.00%
Percentage of over-achievement threshold to which the goals are entitled					100.00%
Percentage Of Over-Achievement To Which Quarterly Performance Based Vesting Cannot Exceed					200.00%
Percentage Of Annual Performance Stock Grant Based On Achieving Annual Revenue Goal					50.00%
Percentage Of Annual Revenue Goal To Be Achieved For Performance Stock Grant					80.00%
Percentage Of Annual Performance Stock Grant Based On Achieving Annual Increase in Stand-alone Software Goal					25.00%
Percentage Of Annual Increase in Stand-alone Software Goal To Be Achieved For Performance Stock Grant					18.00%
Percentage Of Annual Performance Stock Grant Based On Achieving Relative Total Shareholder Return Benchmarked to the S&P 500 Index Goal					25.00%
Percentage Of Over-Achievement To Which Annual Performance Based Vesting Cannot Exceed					200.00%
Annual Equity Program [Member] | November 1, 2018 [Member] | Restricted Stock Units (RSUs) [Member]
Stock-Based Compensation
Approved RSUs to employees and executive officers pursuant to the Company's annual equity awards program | shares							144,066
Annual equity awards program vesting period				3 years
Annual Equity Program [Member] | November 1, 2017 [Member] | Restricted Stock Units (RSUs) [Member]
Stock-Based Compensation
Approved RSUs to employees and executive officers pursuant to the Company's annual equity awards program | shares							140,135
Annual equity awards program vesting period				4 years
Annual Equity Program [Member] | November 1, 2016 [Member] | Restricted Stock Units (RSUs) [Member]
Stock-Based Compensation
Approved RSUs to employees and executive officers pursuant to the Company's annual equity awards program | shares							115,347
Annual equity awards program vesting period				4 years
Annual Equity Program [Member] | November 2, 2015 [Member] | Restricted Stock Units (RSUs) [Member]
Stock-Based Compensation
Approved RSUs to employees and executive officers pursuant to the Company's annual equity awards program | shares							145,508
Annual equity awards program vesting period				4 years
Software and Software Development Costs [Member] | Minimum [Member]
Revenue Recognition
Finite-Lived Intangible Asset, Useful Life				3 years
Software and Software Development Costs [Member] | Maximum [Member]
Revenue Recognition
Finite-Lived Intangible Asset, Useful Life				5 years
Maintenance [Member]
Common Stock Repurchase
Capitalized contract cost, amortization period		4 years 6 months		4 years 6 months	4 years 6 months	4 years 6 months	4 years 6 months	4 years 6 months	4 years 6 months
Subscription and Circulation [Member]
Common Stock Repurchase
Capitalized contract cost, amortization period		3 years		3 years	3 years	3 years	3 years	3 years	3 years