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Stock-based Compensation Plans (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2018 | Dec. 14, 2011
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount | 578,005 | 267,298 | 106,896 |  |
Weighted-average recognition period, Compensation expense related to stock awards not yet vested | 1 year 4 months 24 days |  |  |  |
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount | $ 8.6 |  |  |  |
Number of shares authorized under a Plan |  |  |  |  | 20,500,000
Shares available for future grants under a Plan | 5,806,070 |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period | 10 years |  |  |  |
Share-based Compensation, Expected Forfeiture Rate | 2.00% |  |  |  |
Phantom Share Units (PSUs) [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period | 3 years |  |  |  |
Settlement of performance-based restricted stock units, net of shares withheld for taxes | 131,182 | 118,908 | 132,289 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | 185,808 | 188,973 | 180,747 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value | $ 11.51 | $ 11.16 | $ 11.61 | $ 12.12 |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instrument Other than Option, Nonvested, Intrinsic Value | $ 15.22 |  |  |  |
Share-based compensation liability | $ 3.5 |  |  |  |
Employee Stock [Member] |  |  |  |  |
Number of shares authorized under a Plan |  |  | 5,800,000 |  |
Shares available for future grants under a Plan | 2,254,023 |  |  |  |
Price for shares offered under ESPP, as a percentage of closing price on the first or last day of the offering period | 85.00% |  |  |  |
Performance Shares [Member] |  |  |  |  |
Settlement of performance-based restricted stock units, net of shares withheld for taxes | 103,058,000,000 | 93,647 |  |  |
Restricted Stock Units (RSUs) [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period | 3 years |  |  |  |
Settlement of performance-based restricted stock units, net of shares withheld for taxes | 228,121 | 295,241 | 259,107 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | 220,795 | 301,979 | 233,830 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value | $ 11.78 | $ 11.41 | $ 11.31 | $ 12.14 |
Minimum [Member] | Performance Shares [Member] |  |  |  |  |
Performance Factor | 0.00% |  |  |  |
Maximum [Member] | Performance Shares [Member] |  |  |  |  |
Performance Factor | 200.00% |  |  |  |

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- Definition The number of grants made 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). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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