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Stock-Based Compensation - Narrative (Details) - USD ($) |  | 12 Months Ended
--- | --- | ---
Oct. 31, 2025 | Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Share-based Payment Arrangement, Expense |  | $ 231,500,000 | $ 219,100,000 | $ 236,700,000
Share-based Payment Arrangement, Expense, Tax Benefit |  | 49,900,000 | $ 44,400,000 | $ 44,700,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount |  | $ 229,000,000.0 |  |
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition |  | 2 years |  |
Weighted Average Grant Date Fair Value |  | $ 251.46 | $ 155.99 | $ 144.78
Fair market value of restricted stock vested |  | $ 322,700,000 | $ 228,100,000 | $ 195,900,000
Total intrinsic value of options exercised |  | $ 5,900,000 | $ 7,500,000 | $ 6,900,000
Restricted Stock Units (RSUs) [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Award vesting period |  | 2 years | 2 years | 2 years
Executive Officer Restricted Stock Units (RSUs) | Subsequent Event [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Equity Instruments Other than Options, Grants in Period | 81,099 |  |  |
Two Thousand Eleven Employee Stock Purchase Plan [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Common stock reserved for issuance |  | 12,000,000 |  |
Percentage of base compensation for which employees can acquire shares of common stock |  | 15.00% |  |
Maximum shares allowed for purchase by employee in period |  | 10,000 |  |
Maximum aggregate fair value of stock that an employee may purchase |  | $ 25,000 |  |
Expected term (in years) |  | 6 months |  |
Percentage of common stock lesser of the fair market value |  | 85.00% |  |
Number of Shares Authorized |  | 1,666,569 |  |
Two Thousand Fourteen Equity Incentive Plan [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Common stock reserved for issuance |  | 27,880,000 |  |
Number of Shares Authorized |  | 2,922,335 |  |
Vesting rate of stock options and awards upon certain changes in ownership control |  | 50.00% |  |
Two Thousand Fourteen Equity Incentive Plan [Member] | Performance Shares [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Equity Instruments Other than Options, Grants in Period |  | 120,235 |  |
Outstanding stock units |  | 183,723 | 213,776 |
Shares Issued in Period |  | 120,235 |  |
Weighted Average Grant Date Fair Value |  | $ 220.40 | $ 155.63 |
Two Thousand Fourteen Equity Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Equity Instruments Other than Options, Grants in Period |  | 1,167,667 |  |
Outstanding stock units |  | 1,197,528 | 1,312,328 |
Shares Issued in Period |  | 1,167,667 |  |
Weighted Average Grant Date Fair Value |  | $ 234.22 | $ 158.22 |
Nginx Acquisition Equity Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Outstanding stock units |  | 19 |  |
Threat Stack Acquisition Equity Incentive Plan | Restricted Stock Units (RSUs) [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Outstanding stock units |  | 174 |  |
Lilac Acquisition Equity Incentive Plan | Restricted Stock Units (RSUs) [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Outstanding stock units |  | 9,341 |  |
Nginx, Inc. 2011 Share Plan [Member] | Share-based Payment Arrangement, Option [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Shares available for purchase under stock option plan |  | 1,985 |  |
Shape 2011 Share Plan [Member] | Share-based Payment Arrangement, Option [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Shares available for purchase under stock option plan |  | 18,965 |  |
Volterra 2017 Stock Plan | Share-based Payment Arrangement, Option [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Shares available for purchase under stock option plan |  | 6,005 |  |
Lilac Cloud 2018 Equity Incentive Plan | Share-based Payment Arrangement, Option [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Shares available for purchase under stock option plan |  | 525 |  |

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