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Stock-based Compensation Plans (Narrative) (Details) $ / shares in Units, $ in Millions |  |  |  | 3 Months Ended | 6 Months Ended
--- | --- | --- | --- | --- | ---
Feb. 24, 2020 $ / shares shares | Jan. 28, 2020 $ / shares shares | Dec. 03, 2019 $ / shares shares | Mar. 31, 2020 USD ($) $ / shares shares | Dec. 31, 2019 $ / shares shares | Mar. 31, 2019 USD ($) shares | Mar. 31, 2020 USD ($) $ / shares shares | Mar. 31, 2019 USD ($) shares
Share-based Payment Arrangement, Expense | $ |  |  |  | $ 1.3 |  | $ 1.0 | $ 3.2 | $ 2.7
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount | $ |  |  |  | $ 10.4 |  |  | $ 10.4 |
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount |  |  |  | 267,697 |  | 202,245 | 184,296 | 1,077,983
Phantom Share Units (PSUs) [Member] |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instrument Other than Option, Nonvested, Intrinsic Value | $ / shares |  |  |  | $ 8.01 |  |  | $ 8.01 |
Share-based compensation liability | $ |  |  |  | $ 1.0 |  |  | $ 1.0 |
Granted, shares |  |  |  |  | 188,973 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | $ / shares |  |  |  |  | $ 11.26 |  |  |
Granted, shares |  |  |  |  | 188,973 |  |  |
Performance Shares [Member] |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period |  |  |  |  |  |  | 93,647 | 181,065
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period |  |  |  |  |  |  | 209,966 |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period |  |  |  |  | 3 years |  |  |
Share-based compensation, units awarded but not yet granted |  |  |  | 232,262 |  |  | 232,262 |
Restricted Stock Units (RSUs) [Member] |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period |  |  |  | 114,691 |  |  | 246,994 |
Granted, shares |  |  |  | 118,684 | 162,433 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | $ / shares |  |  |  | $ 12.14 | $ 11.26 |  |  |
Granted, shares |  |  |  | 118,684 | 162,433 |  |  |
Market Based Performance Shares |  |  |  |  |  |  |  |
Granted, shares | 7,498 | 2,763 | 147,213 | 10,261 | 147,213 |  | 157,474 |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate | 1730000.00% | 1760000.00% | 1870000.00% |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | $ / shares | $ 18.17 | $ 16.76 | $ 14.94 | $ 17.79 | $ 14.94 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate | 1230000.00% | 1440000.00% | 1530000.00% |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term | 2 years 7 months 6 days | 2 years 8 months 1 day | 2 years 9 months 29 days |  |  |  |  |
Granted, shares | 7,498 | 2,763 | 147,213 | 10,261 | 147,213 |  | 157,474 |
Minimum [Member] | Performance Shares [Member] |  |  |  |  |  |  |  |
Performance Factors |  |  |  |  |  |  | 0 |
Minimum [Member] | Market Based Performance Shares |  |  |  |  |  |  |  |
Performance Factors |  |  |  |  |  |  | 0 |
Maximum [Member] | Performance Shares [Member] |  |  |  |  |  |  |  |
Performance Factors |  |  |  |  |  |  | 2 |
Maximum [Member] | Market Based Performance Shares |  |  |  |  |  |  |  |
Performance Factors |  |  |  |  |  |  | 2 |
Share-based Payment Arrangement, Tranche One [Member] | Performance Shares [Member] |  |  |  |  |  |  |  |
Granted, shares |  |  |  | 13,682 | 65,428 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | $ / shares |  |  |  | $ 12.09 | $ 11.26 |  |  |
Granted, shares |  |  |  | 13,682 | 65,428 |  |  |
Share-based Payment Arrangement, Tranche Two [Member] | Performance Shares [Member] |  |  |  |  |  |  |  |
Granted, shares |  |  |  |  | 102,203 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | $ / shares |  |  |  |  | $ 11.26 |  |  |
Granted, shares |  |  |  |  | 102,203 |  |  |
Share-based Payment Arrangement, Tranche Three [Member] | Performance Shares [Member] |  |  |  |  |  |  |  |
Granted, shares |  |  |  |  | 44,451 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | $ / shares |  |  |  |  | $ 11.26 |  |  |
Granted, shares |  |  |  |  | 44,451 |  |  |

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