Equity Incentive Plan (Narrative) (Details) $ / shares in Units, shares in Millions	12 Months Ended
Sep. 30, 2019 USD ($) shares / unit $ / shares shares	Sep. 30, 2018 USD ($) $ / shares shares	Sep. 30, 2017 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock issuable per restricted stock unit \| shares / unit	1
Share-based Payment Arrangement, Noncash Expense	$ 86,400,000	$ 82,939,000	$ 76,708,000
Total unrecognized compensation cost	$ 159,200,000
Weighted average remaining recognition period, in months	22 months
Common stock were available for grant under the 2000 plan \| shares	6.9
Common stock were reserved for issuance \| shares	3.2
ESPP maximum contribution percentage	10.00%
ESPP maximum contribution amount by employee	$ 25,000
ESPP purchase price as a % of stock price	85.00%
Shares withheld for tax withholding obligation \| shares	0.5	0.7	0.5
Payments of withholding taxes in connection with vesting of stock-based awards	$ 44,366,000	$ 45,374,000	$ 26,654,000
Restricted Shares and Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average fair value per share \| $ / shares	$ 82.77	$ 76.17	$ 51.27
Employee Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Payment Arrangement, Noncash Expense	$ 6,200,000	$ 4,300,000	$ 3,200,000
TSR Units [Member] \| Restricted Shares and Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average fair value per share \| $ / shares	$ 4.62	$ 4.35	$ 2.27

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Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Common Stock Issuable per Restricted Stock Unit

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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Amount of cash outflow to satisfy grantee's tax withholding obligation for award under share-based payment arrangement.

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Amount of noncash expense for share-based payment arrangement.

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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Weighted average remaining contractual term for equity-based awards excluding options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The highest percentage of annual salary that an employee is permitted to utilize with respect to the plan.

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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The number of shares reserved for issuance pertaining to the outstanding exercisable stock options as of the balance sheet date in the customized range of exercise prices for which the market and performance vesting condition has been satisfied.

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Purchase price of common stock expressed as a percentage of its fair value.

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Number of shares used to settle grantee's tax withholding obligation for award under share-based payment arrangement.

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