Summary of Significant Accounting Policies (Policies)	12 Months Ended
Sep. 30, 2017
Accounting Policies [Abstract]
Revenue Recognition	Revenue Recognition-Revenue is recognized when delivery of products has occurred or services have been rendered and there is persuasive evidence of a sales arrangement, selling prices are fixed or determinable and collectibility is reasonably assured. Revenue is reported net of estimated discounts, returns and rebates as “net sales.” In May 2014, the Financial Accounting Standards Board (“FASB”) issued new guidance for the recognition of revenue and requiring additional financial statement disclosures. We plan to adopt this guidance using the modified retrospective transition method beginning in the first quarter of fiscal 2019. We have completed our initial scoping and are developing a project plan to classify our revenue streams, to evaluate revenue recognition practices for each stream against the new requirements, to consider changes to the terms of our sales contracts, and to design and implement processes to quantify the effects of necessary changes. This work is ongoing, but at this time, we do not expect the new guidance to materially impact our stockholders' equity, net sales or operating income.
Share-based Compensation	Stock-based Compensation-Compensation expense for stock-based awards granted to employees and directors is based on the fair value at the grant dates for our stock-settled share awards and is based on the fair value at each reporting date for our cash-settled share awards. See Note 11. for more information regarding our stock-based compensation. Stock-based compensation expense is a component of selling, general and administrative expenses. At March 31, 2016, we adopted FASB Accounting Standards Update 2016-09 Improvements to Employee Share-Based Payment Accounting. Most significantly, this update changes the accounting for “excess tax benefits” related to stock-based compensation awards by requiring such benefits be included in earnings, rather than recorded directly to additional paid-in capital.
Cash and Cash Equivalents	Cash and Cash Equivalents-All highly liquid investments with remaining maturities of 90 days or less when purchased are classified as cash equivalents. Where there is no right of offset against cash balances, outstanding checks are included in accounts payable.
Receivables	Receivables-Receivables are amounts due from customers. To reduce credit risk, credit investigations are generally performed prior to accepting orders from new customers and, when necessary, letters of credit, bonds or other instruments are required to ensure payment. We present trade receivables net of an allowance for credit losses. Our consolidated statements of operations reflect the measurement of credit losses for newly recognized trade receivables, as well as the expected increases or decreases of expected credit losses that have taken place during the period. Our periodic evaluations of expected credit losses are based upon our judgments regarding prior collection experience, specific customer creditworthiness, other current conditions and forecasts of current economic trends within the industries served that may affect the collectibility of the reported amounts. Significantly weaker than anticipated industry or economic conditions could impact customers’ ability to pay such that actual credit losses may be greater than the amounts provided for in this allowance. When we determine a specific trade receivable will not be collected, we charge off the uncollectible amount against the allowance.
Inventory Supplies, Policy	Other Current Assets-Other current assets include maintenance supplies and tooling costs. Costs for perishable tools and maintenance items are expensed when put into service. Costs for more durable items are amortized over their estimated useful lives, ranging from 3 to 10 years.
Inventories	Inventories-Inventories are recorded at the lower of first-in, first-out method cost or estimated net realizable value. We evaluate our inventory in terms of excess and obsolete exposures. This evaluation includes such factors as anticipated usage, inventory turnover, inventory levels and ultimate product sales value. Inventory cost includes an overhead component that is affected by levels of production and actual costs incurred. We periodically evaluate the effects of production levels and costs capitalized as part of inventory.
Property, Plant and Equipment	Property, Plant and Equipment-Property, plant and equipment is recorded at cost, less accumulated depreciation. Depreciation is recorded using the straight-line method over the estimated useful lives of the assets. Estimated useful lives are 10 to 20 years for land improvements, 10 to 40 years for buildings and 3 to 15 years for machinery and equipment. Leasehold improvements and capitalized leases are depreciated using the straight-line method over the lesser of the useful life of the asset or the remaining lease term. Gains and losses upon disposition are reflected in operating results in the period of disposition. Direct internal and external costs to implement computer systems and internal-use software are capitalized. Capitalized costs are depreciated over the estimated useful life of the system or software, generally 6 years, beginning when site installation or module development is complete and ready for use. Liabilities are recognized at fair value for asset retirement obligations related to plant and landfill closures in the period in which they are reasonably estimable and the carrying amounts of the related long-lived assets are correspondingly increased. Over time, the liabilities are accreted to their estimated future values. At September 30, 2017 and 2016, asset retirement obligations were $3.8 million and $7.5 million, respectively. During 2016, FASB issued Accounting Standards Update 2016-02 Leases, which will require us to recognize lease assets and lease liabilities for those leases currently referred to as operating leases. This requirement is effective for 2020, although early adoption is permitted. The update allows for several different methods of application and adoption of the requirement. We are currently evaluating these methods, in what period we will adopt the requirement, and the impact of this requirement, which we do not believe will be material to our consolidated financial statements as a whole.
Accounting for the Impairment of Long-Lived Assets	Accounting for the Impairment of Long-Lived Assets-We test indefinite-lived intangible assets and goodwill for impairment annually (or more frequently if events or circumstances indicate possible impairment.) We perform our annual impairment testing at September 1. We amortize finite-lived intangible assets over their respective estimated useful lives and review for impairment if events or circumstances indicate possible impairment.
Workers Compensation	Workers Compensation-Our exposure to workers compensation claims is generally limited to $1 million per incident. Liabilities, including those related to claims incurred but not reported, are recorded principally using annual valuations based on discounted future expected payments and using historical data combined with insurance industry data when historical data is limited. We are indemnified under an agreement with a predecessor to Tyco for all Mueller Co. and Anvil workers compensation liabilities related to incidents that occurred prior to August 16, 1999. See Note 17. We retained U.S. Pipe workers compensation liabilities related to incidents that occurred prior to the segment's April 1, 2012 sale date, but the purchaser agreed to reimburse us for up to $11.8 million in payments we make related to these liabilities. At September 30, 2017, the remaining reimbursements may be up to $4.1 million, which we have recorded on a discounted basis as $0.5 million in other current assets and $3.6 million in other noncurrent assets. On an undiscounted basis, workers compensation liabilities were $10.7 million and $13.7 million at September 30, 2017 and 2016, respectively. On a discounted basis, workers compensation liabilities were $9.1 million and $11.8 million at September 30, 2017 and 2016, respectively. We apply a discount rate at a risk-free interest rate, generally a U.S. Treasury bill rate, for each policy period. The rate used is one with a duration that corresponds to the weighted average expected payout period for each policy period. Once a discount rate is applied to a policy period, it remains the discount rate for that policy period until all claims are paid.
Warranty Costs	Warranty Costs-We accrue for warranty expenses that can include customer costs of repair and/or replacement, including labor, materials, equipment, freight and reasonable overhead costs. We accrue for the estimated cost of product warranties at the time of sale if such costs are determined to be reasonably estimable at that time. Warranty cost estimates are revised throughout applicable warranty periods as better information regarding warranty costs becomes available.
Deferred Financing Fees	Deferred Financing Costs-Costs of debt financing are charged to expense over the lives of the related financing agreements. Remaining costs and the future period over which they would be charged to expense are reassessed when amendments to the related financing agreements or prepayments occur. ABL Agreement deferred financing costs are included in other noncurrent assets and other deferred financing costs are offset against long-term debt in the accompanying consolidated balance sheets. Deferred financing costs of $7.4 million at September 30, 2017 are scheduled to amortize as follows: $1.5 million related to the ABL Agreement amortizes on a straight-line basis; $5.9 million related to the Term Loan amortizes using the effective-interest rate method. All such amortization will be over the remaining term of the respective debt.
Derivative Instruments and Hedging Activities	Derivative Instruments and Hedging Activities-We manage interest rate risk to some extent using derivative instruments. We designated our interest rate swap contracts as cash flow hedges of interest payments. As a result, the changes in the fair value of these contracts prior to settlement are reported as a component of accumulated other comprehensive loss and are reclassified into earnings in the periods during which the hedged transactions affect earnings.
Income Taxes	Income Taxes-Deferred tax liabilities and deferred tax assets are recognized for the expected future tax consequences of events that have been included in the financial statements or tax returns. Such liabilities and assets are determined based on the differences between the financial statement basis and the tax basis of assets and liabilities, using tax rates in effect for the years in which the differences are expected to reverse. A valuation allowance is provided when, based upon the available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. We only record tax benefits for positions that management believes are more likely than not of being sustained under audit based solely on the technical merits of the associated tax position. The amount of tax benefit recognized for any position that meets the more likely than not threshold is the largest amount of the tax benefit that we believe is greater than 50% likely of being realized.
Environmental Expenditures	Environmental Expenditures-We capitalize environmental expenditures that increase the life or efficiency of noncurrent assets or that reduce or prevent environmental contamination. We accrue for environmental expenses resulting from existing conditions that relate to past operations when the costs are probable and reasonably estimable. We are indemnified under an agreement with a predecessor to Tyco for certain environmental liabilities that existed at August 16, 1999. See Note 17.
Research and Development	Research and Development-Research and development costs are expensed as incurred.
Advertising	Advertising-Advertising costs are expensed as incurred.
Translation of Foreign Currency	Translation of Foreign Currency-Assets and liabilities of our businesses whose functional currency is other than the U.S. dollar are translated into U.S. dollars using currency exchange rates at the balance sheet date. Revenues and expenses are translated at average currency exchange rates during the period. Foreign currency translation gains and losses are reported as a component of accumulated other comprehensive loss. Gains and losses resulting from foreign currency transactions are included in operating results as incurred.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Sep. 30, 2017

Revenue Recognition-Revenue is recognized when delivery of products has occurred or services have been rendered and there is persuasive evidence of a sales arrangement, selling prices are fixed or determinable and collectibility is reasonably assured. Revenue is reported net of estimated discounts, returns and rebates as “net sales.”

In May 2014, the Financial Accounting Standards Board (“FASB”) issued new guidance for the recognition of revenue and requiring additional financial statement disclosures. We plan to adopt this guidance using the modified retrospective transition method beginning in the first quarter of fiscal 2019. We have completed our initial scoping and are developing a project plan to classify our revenue streams, to evaluate revenue recognition practices for each stream against the new requirements, to consider changes to the terms of our sales contracts, and to design and implement processes to quantify the effects of necessary changes. This work is ongoing, but at this time, we do not expect the new guidance to materially impact our stockholders' equity, net sales or operating income.

Share-based Compensation

Stock-based Compensation-Compensation expense for stock-based awards granted to employees and directors is based on the fair value at the grant dates for our stock-settled share awards and is based on the fair value at each reporting date for our cash-settled share awards. See Note 11. for more information regarding our stock-based compensation. Stock-based compensation expense is a component of selling, general and administrative expenses.

At March 31, 2016, we adopted FASB Accounting Standards Update 2016-09 Improvements to Employee Share-Based Payment Accounting. Most significantly, this update changes the accounting for “excess tax benefits” related to stock-based compensation awards by requiring such benefits be included in earnings, rather than recorded directly to additional paid-in capital.

Cash and Cash Equivalents

Cash and Cash Equivalents-All highly liquid investments with remaining maturities of 90 days or less when purchased are classified as cash equivalents. Where there is no right of offset against cash balances, outstanding checks are included in accounts payable.

Receivables

Receivables-Receivables are amounts due from customers. To reduce credit risk, credit investigations are generally performed prior to accepting orders from new customers and, when necessary, letters of credit, bonds or other instruments are required to ensure payment.

We present trade receivables net of an allowance for credit losses. Our consolidated statements of operations reflect the measurement of credit losses for newly recognized trade receivables, as well as the expected increases or decreases of expected credit losses that have taken place during the period.

Our periodic evaluations of expected credit losses are based upon our judgments regarding prior collection experience, specific customer creditworthiness, other current conditions and forecasts of current economic trends within the industries served that may affect the collectibility of the reported amounts. Significantly weaker than anticipated industry or economic conditions could impact customers’ ability to pay such that actual credit losses may be greater than the amounts provided for in this allowance.

When we determine a specific trade receivable will not be collected, we charge off the uncollectible amount against the allowance.

Inventory Supplies, Policy

Other Current Assets-Other current assets include maintenance supplies and tooling costs. Costs for perishable tools and maintenance items are expensed when put into service. Costs for more durable items are amortized over their estimated useful lives, ranging from 3 to 10 years.

Inventories

Inventories-Inventories are recorded at the lower of first-in, first-out method cost or estimated net realizable value. We evaluate our inventory in terms of excess and obsolete exposures. This evaluation includes such factors as anticipated usage, inventory turnover, inventory levels and ultimate product sales value. Inventory cost includes an overhead component that is affected by levels of production and actual costs incurred. We periodically evaluate the effects of production levels and costs capitalized as part of inventory.

Property, Plant and Equipment

Property, Plant and Equipment-Property, plant and equipment is recorded at cost, less accumulated depreciation. Depreciation is recorded using the straight-line method over the estimated useful lives of the assets. Estimated useful lives are 10 to 20 years for land improvements, 10 to 40 years for buildings and 3 to 15 years for machinery and equipment. Leasehold improvements and capitalized leases are depreciated using the straight-line method over the lesser of the useful life of the asset or the remaining lease term. Gains and losses upon disposition are reflected in operating results in the period of disposition.

Direct internal and external costs to implement computer systems and internal-use software are capitalized. Capitalized costs are depreciated over the estimated useful life of the system or software, generally 6 years, beginning when site installation or module development is complete and ready for use.

Liabilities are recognized at fair value for asset retirement obligations related to plant and landfill closures in the period in which they are reasonably estimable and the carrying amounts of the related long-lived assets are correspondingly increased. Over time, the liabilities are accreted to their estimated future values. At September 30, 2017 and 2016, asset retirement obligations were $3.8 million and $7.5 million, respectively.

During 2016, FASB issued Accounting Standards Update 2016-02 Leases, which will require us to recognize lease assets and lease liabilities for those leases currently referred to as operating leases. This requirement is effective for 2020, although early adoption is permitted. The update allows for several different methods of application and adoption of the requirement. We are currently evaluating these methods, in what period we will adopt the requirement, and the impact of this requirement, which we do not believe will be material to our consolidated financial statements as a whole.

Accounting for the Impairment of Long-Lived Assets

Accounting for the Impairment of Long-Lived Assets-We test indefinite-lived intangible assets and goodwill for impairment annually (or more frequently if events or circumstances indicate possible impairment.) We perform our annual impairment testing at September 1. We amortize finite-lived intangible assets over their respective estimated useful lives and review for impairment if events or circumstances indicate possible impairment.

Workers Compensation

Workers Compensation-Our exposure to workers compensation claims is generally limited to $1 million per incident. Liabilities, including those related to claims incurred but not reported, are recorded principally using annual valuations based on discounted future expected payments and using historical data combined with insurance industry data when historical data is limited. We are indemnified under an agreement with a predecessor to Tyco for all Mueller Co. and Anvil workers compensation liabilities related to incidents that occurred prior to August 16, 1999. See Note 17. We retained U.S. Pipe workers compensation liabilities related to incidents that occurred prior to the segment's April 1, 2012 sale date, but the purchaser agreed to reimburse us for up to $11.8 million in payments we make related to these liabilities. At September 30, 2017, the remaining reimbursements may be up to $4.1 million, which we have recorded on a discounted basis as $0.5 million in other current assets and $3.6 million in other noncurrent assets. On an undiscounted basis, workers compensation liabilities were $10.7 million and $13.7 million at September 30, 2017 and 2016, respectively. On a discounted basis, workers compensation liabilities were $9.1 million and $11.8 million at September 30, 2017 and 2016, respectively.

We apply a discount rate at a risk-free interest rate, generally a U.S. Treasury bill rate, for each policy period. The rate used is one with a duration that corresponds to the weighted average expected payout period for each policy period. Once a discount rate is applied to a policy period, it remains the discount rate for that policy period until all claims are paid.

Warranty Costs

Warranty Costs-We accrue for warranty expenses that can include customer costs of repair and/or replacement, including labor, materials, equipment, freight and reasonable overhead costs. We accrue for the estimated cost of product warranties at the time of sale if such costs are determined to be reasonably estimable at that time. Warranty cost estimates are revised throughout applicable warranty periods as better information regarding warranty costs becomes available.

Deferred Financing Fees

Deferred Financing Costs-Costs of debt financing are charged to expense over the lives of the related financing agreements. Remaining costs and the future period over which they would be charged to expense are reassessed when amendments to the related financing agreements or prepayments occur.

ABL Agreement deferred financing costs are included in other noncurrent assets and other deferred financing costs are offset against long-term debt in the accompanying consolidated balance sheets. Deferred financing costs of $7.4 million at September 30, 2017 are scheduled to amortize as follows: $1.5 million related to the ABL Agreement amortizes on a straight-line basis; $5.9 million related to the Term Loan amortizes using the effective-interest rate method. All such amortization will be over the remaining term of the respective debt.

Derivative Instruments and Hedging Activities

Derivative Instruments and Hedging Activities-We manage interest rate risk to some extent using derivative instruments. We designated our interest rate swap contracts as cash flow hedges of interest payments. As a result, the changes in the fair value of these contracts prior to settlement are reported as a component of accumulated other comprehensive loss and are reclassified into earnings in the periods during which the hedged transactions affect earnings.

Income Taxes

Income Taxes-Deferred tax liabilities and deferred tax assets are recognized for the expected future tax consequences of events that have been included in the financial statements or tax returns. Such liabilities and assets are determined based on the differences between the financial statement basis and the tax basis of assets and liabilities, using tax rates in effect for the years in which the differences are expected to reverse. A valuation allowance is provided when, based upon the available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized.

We only record tax benefits for positions that management believes are more likely than not of being sustained under audit based solely on the technical merits of the associated tax position. The amount of tax benefit recognized for any position that meets the more likely than not threshold is the largest amount of the tax benefit that we believe is greater than 50% likely of being realized.

Environmental Expenditures

Environmental Expenditures-We capitalize environmental expenditures that increase the life or efficiency of noncurrent assets or that reduce or prevent environmental contamination. We accrue for environmental expenses resulting from existing conditions that relate to past operations when the costs are probable and reasonably estimable. We are indemnified under an agreement with a predecessor to Tyco for certain environmental liabilities that existed at August 16, 1999. See Note 17.

Research and Development

Research and Development-Research and development costs are expensed as incurred.

Advertising

Advertising-Advertising costs are expensed as incurred.

Translation of Foreign Currency

Translation of Foreign Currency-Assets and liabilities of our businesses whose functional currency is other than the U.S. dollar are translated into U.S. dollars using currency exchange rates at the balance sheet date. Revenues and expenses are translated at average currency exchange rates during the period. Foreign currency translation gains and losses are reported as a component of accumulated other comprehensive loss. Gains and losses resulting from foreign currency transactions are included in operating results as incurred.