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Summary of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2016 | Jan. 06, 2017 | Sep. 30, 2014
Gain (Loss) on Discontinuation of Interest Rate Cash Flow Hedge Due to Forecasted Transaction Probable of Not Occurring, Net | $ 2.4 | $ 0.0 | $ 0.0 |  |
Product Warranty Expense | 18.7 | 12.3 | $ 5.3 |  |
Asset Retirement Obligation | 4.1 | 3.8 |  |  |
Exposure to Workers Compensation Claims, Per Incident | 1.0 |  |  |  |
Discontinued Operations, Receivable from Buyer of Discontinued Operation |  |  |  | $ 1.9 | $ 11.8
Workers Compensation Undiscounted Basis Liability | 9.1 | 10.7 |  |  |
Workers' Compensation Liability | $ 7.7 | 9.1 |  |  |
Income Tax Benefit, Likelihood of Realization Threshold | 50.00% |  |  |  |
Debt Issuance Costs, Net | $ 7.4 |  |  |  |
Minimum [Member] |  |  |  |  |
Finite-Lived Tangible Asset, Useful Life, Maximum | 3 years |  |  |  |
Maximum [Member] |  |  |  |  |
Finite-Lived Tangible Asset, Useful Life, Maximum | 10 years |  |  |  |
Land Improvements [Member] | Minimum [Member] |  |  |  |  |
Property, Plant and Equipment, Useful Life, Minimum | 10 years |  |  |  |
Land Improvements [Member] | Maximum [Member] |  |  |  |  |
Property, Plant and Equipment, Useful Life, Minimum | 20 years |  |  |  |
Building [Member] | Minimum [Member] |  |  |  |  |
Property, Plant and Equipment, Useful Life, Minimum | 10 years |  |  |  |
Building [Member] | Maximum [Member] |  |  |  |  |
Property, Plant and Equipment, Useful Life, Minimum | 40 years |  |  |  |
Machinery and Equipment [Member] | Minimum [Member] |  |  |  |  |
Property, Plant and Equipment, Useful Life, Minimum | 3 years |  |  |  |
Machinery and Equipment [Member] | Maximum [Member] |  |  |  |  |
Property, Plant and Equipment, Useful Life, Minimum | 15 years |  |  |  |
Software and Software Development Costs [Member] | Maximum [Member] |  |  |  |  |
Property, Plant and Equipment, Useful Life, Minimum | 6 years |  |  |  |
U.S. Pipe [Member] | Maximum [Member] |  |  |  |  |
Discontinued Operations, Receivable from Buyer of Discontinued Operation |  | 4.5 |  |  |
Other Current Assets [Member] | U.S. Pipe [Member] |  |  |  |  |
Discontinued Operations, Receivable from Buyer of Discontinued Operation |  | 1.2 |  |  |
Other Noncurrent Assets [Member] | U.S. Pipe [Member] |  |  |  |  |
Discontinued Operations, Receivable from Buyer of Discontinued Operation |  | 3.3 |  |  |
Revolving Credit Facility [Member] |  |  |  |  |
Debt Issuance Costs, Net | $ 0.8 |  |  |  |
Secured Debt [Member] |  |  |  |  |
Debt Issuance Costs, Net | 6.6 | 5.9 |  |  |
Unsecured Debt [Member] |  |  |  |  |
Debt Issuance Costs, Net | 6.6 |  |  |  |
Product Concentration Risk [Member] |  |  |  |  |
Product Warranty Expense | $ 14.1 | $ 9.8 |  |  |

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