Beacon Roofing Supply (BECN) 10-K 21 Nov 17 2017 FY Annual report Financial data

Document And Entity Information

Document And Entity Information - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Oct. 31, 2017	Mar. 31, 2017
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Sep. 30, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Trading Symbol	BECN
Entity Registrant Name	BEACON ROOFING SUPPLY INC
Entity Central Index Key	1,124,941
Current Fiscal Year End Date	--09-30
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 2,960
Entity Common Stock, Shares Outstanding		67,734,465

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2017	Sep. 30, 2016
Current assets:
Cash and cash equivalents	$ 138,250	$ 31,386
Accounts receivable, less allowance of $11,829 and $14,182 as of September 30, 2017 and 2016, respectively	704,527	626,965
Inventories, net	551,924	480,736
Prepaid expenses and other current assets	209,138	163,103
Total current assets	1,603,839	1,302,190
Property and equipment, net	156,129	148,569
Goodwill	1,251,986	1,197,565
Intangibles, net	429,069	464,024
Other assets, net	8,534	1,511
Total Assets	3,449,557	3,113,859
Current liabilities:
Accounts payable	503,697	360,915
Accrued expenses	261,297	161,113
Current portions of long-term debt	14,141	14,811
Total current liabilities	779,135	536,839
Borrowings under revolving lines of credit, net	3,205	359,661
Long-term debt, net	721,268	722,929
Deferred income taxes, net	138,383	135,482
Long-term obligations under equipment financing and other, net	25,760	35,121
Total liabilities	1,667,751	1,790,032
Commitments and contingencies
Stockholders' equity:
Common stock (voting); $.01 par value; 100,000,000 shares authorized; 67,700,858 issued and outstanding as of September 30, 2017 and 59,890,885 issued and outstanding as of September 30, 2016	677	598
Undesignated preferred stock; 5,000,000 shares authorized, none issued or outstanding	0	0
Additional paid-in capital	1,047,506	694,564
Retained earnings	748,186	647,322
Accumulated other comprehensive loss	(14,563)	(18,657)
Total stockholders' equity	1,781,806	1,323,827
Total Liabilities and Stockholders' Equity	$ 3,449,557	$ 3,113,859

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2017	Sep. 30, 2016
Statement Of Financial Position [Abstract]
Accounts receivable, allowances	$ 11,829	$ 14,182
Common stock (voting), par value	$ 0.01	$ 0.01
Common stock (voting), shares authorized	100,000,000	100,000,000
Common Stock (Voting), issued	67,700,858	59,890,885
Common Stock (voting), outstanding	67,700,858	59,890,885
Undesignated Preferred Stock, shares authorized	5,000,000	5,000,000
Undesignated Preferred Stock, issued	0	0
Undesignated Preferred Stock, outstanding	0	0

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Income Statement [Abstract]
Net sales	$ 4,376,670	$ 4,127,109	$ 2,515,169
Cost of products sold	3,300,731	3,114,040	1,919,804
Gross profit	1,075,939	1,013,069	595,365
Operating expense	859,843	808,085	478,284
Income from operations	216,096	204,984	117,081
Interest expense, financing costs, and other	52,751	58,452	11,037
Income before provision for income taxes	163,345	146,532	106,044
Provision for income taxes	62,481	56,615	43,767
Net income	$ 100,864	$ 89,917	$ 62,277
Weighted-average common stock outstanding:
Basic	60,315,648	59,424,372	49,578,130
Diluted	61,344,263	60,418,067	50,173,478
Net income per share:
Basic	$ 1.67	$ 1.51	$ 1.26
Diluted	$ 1.64	$ 1.49	$ 1.24

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 100,864	$ 89,917	$ 62,277
Other comprehensive income (loss):
Foreign currency translation adjustment	3,706	1,024	(14,003)
Unrealized loss due to change in fair value of derivatives, net of tax	0	0	(138)
Total other comprehensive income (loss)	3,706	1,024	(14,141)
Comprehensive income	$ 104,570	$ 90,941	$ 48,136

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss)
Balance at Sep. 30, 2014	$ 817,101	$ 493	$ 328,059	$ 495,128	$ (6,579)
Balance (in shares) at Sep. 30, 2014		49,392,774
Issuance of common stock, net of shares withheld for taxes	7,943	$ 4	7,939	0	0
Issuance of common stock, net of shares withheld for taxes (Shares)		397,969
Stock-based compensation	9,936	$ 0	9,936	0	0
Other comprehensive income (loss)	(14,141)	0	0	0	(14,141)
Net income	62,277	0	0	62,277	0
Balance at Sep. 30, 2015	883,116	$ 497	345,934	557,405	(20,720)
Balance (in shares) at Sep. 30, 2015		49,790,743
Issuance of common stock, net of shares withheld for taxes	24,158	$ 11	24,147	0	0
Issuance of common stock, net of shares withheld for taxes (Shares)		1,061,134
Issuance of common stock in connection with RSG acquisition	306,824	$ 90	306,734	0	0
Issuance of common stock in connection with RSG acquisition (shares)		9,039,008
Stock-based compensation	17,749	$ 0	17,749	0	0
Other comprehensive income (loss)	2,063	0	0	0	2,063
Net income	89,917	0	0	89,917	0
Balance at Sep. 30, 2016	1,323,827	$ 598	694,564	647,322	(18,657)
Balance (in shares) at Sep. 30, 2016		59,890,885
Issuance of common stock, net of shares withheld for taxes	8,627	$ 6	8,621	0	0
Issuance of common stock, net of shares withheld for taxes (Shares)		536,223
Issuance of common stock from secondary offering, net of issuance costs	329,323	$ 73	329,250	0	0
Issuance of common stock from secondary offering, net of issuance costs (Shares)		7,273,750
Stock-based compensation	15,071	$ 0	15,071	0	0
Other comprehensive income (loss)	4,094	0	0	0	4,094
Net income	100,864	0	0	100,864	0
Balance at Sep. 30, 2017	$ 1,781,806	$ 677	$ 1,047,506	$ 748,186	$ (14,563)
Balance (in shares) at Sep. 30, 2017		67,700,858

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Operating Activities
Net income	$ 100,864	$ 89,917	$ 62,277
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	116,467	100,191	34,862
Stock-based compensation	15,071	17,749	9,936
Certain interest expense and other financing costs	10,497	8,329	(1,450)
Gain on sale of fixed assets	(839)	(1,882)	(1,107)
Deferred income taxes	393	25,200	17,634
Other, net	0	0	263
Changes in operating assets and liabilities, net of the effects of businesses acquired:
Accounts receivable	(60,185)	(30,408)	(33,251)
Inventories	(51,768)	43,489	(9,203)
Prepaid expenses and other assets	(44,208)	(12,841)	(17,119)
Accounts payable and accrued expenses	228,908	(119,096)	46,498
Net cash provided by operating activities	315,200	120,648	109,340
Investing Activities
Purchases of property and equipment	(39,828)	(26,315)	(20,802)
Acquisition of businesses, net	(129,390)	(1,018,188)	(85,301)
Proceeds from the sale of assets	2,233	1,882	1,389
Net cash used in investing activities	(166,985)	(1,042,621)	(104,714)
Financing Activities
Borrowings under revolving lines of credit	2,464,128	1,892,459	560,634
Repayments under revolving lines of credit	(2,833,230)	(1,541,532)	(566,007)
Borrowings under term loan	0	490,793	0
Repayments under term loan	(4,500)	(230,918)	(11,250)
Borrowings under Senior Notes	0	300,000	0
Repayments under equipment financing facilities and other	(10,034)	(4,724)	(5,553)
Payment of debt issuance costs	(1,669)	(28,325)	0
Proceeds from secondary offering of common stock	345,503	0	0
Payment of issuance costs from secondary offering of common stock	(14,684)	0	0
Proceeds from issuance of common stock related to equity awards	11,341	24,160	7,943
Taxes paid related to net share settlement of equity awards	(392)	(2)	0
Excess tax benefit from stock-based compensation	2,937	4,956	1,526
Net cash provided by (used in) financing activities	(40,600)	906,867	(12,707)
Effect of exchange rate changes on cash and cash equivalents	(751)	831	(730)
Net increase (decrease) in cash and cash equivalents	106,864	(14,275)	(8,811)
Cash and cash equivalents, beginning of period	31,386	45,661	54,472
Cash and cash equivalents, end of period	138,250	31,386	45,661
Cash paid during the period for:
Interest	49,067	57,934	8,276
Income taxes, net of tax refunds	$ 56,158	$ 14,425	$ 23,198

Consolidated Statements of Cas8

Consolidated Statements of Cash Flows (Parenthetical) $ in Millions	12 Months Ended
	Sep. 30, 2016USD ($)
Statement Of Cash Flows [Abstract]
Non Cash or Part Non Cash Acquisition Non Cash Financial Or Equity Instrument Consideration Shares Issued Value	$ 302
Non Cash or Part Non Cash Acquisition Non Cash Financial Or Equity Instrument Consideration Replacement Awards Value	$ 5

Company Overview

Company Overview	12 Months Ended
	Sep. 30, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Company Overview	1. Company Overview Beacon Roofing Supply, Inc. (the “Company”) was incorporated in the state of Delaware on August 22, 1997 and is a leading distributor of residential and non-residential roofing materials and other complementary building materials. The Company operates its business under regional and local trade names and services customers in 48 states within the United States and 6 provinces in Canada. The Company’s current material subsidiaries are Beacon Sales Acquisition, Inc., Beacon Canada, Inc. and Beacon Roofing Supply Canada Company.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All inter-company transactions have been eliminated. Certain prior period amounts have been reclassified to conform to current period presentation. Use of Estimates The preparation of consolidated financial statements in conformity with United States generally accepted accounting principles (“GAAP”) requires management to make estimates and assumptions that affect the amounts reported in these consolidated financial statements and accompanying notes. Significant items subject to such estimates include inventories, purchase price allocations, recoverability of goodwill and intangibles, and income taxes. Actual amounts could differ from those estimates. Fiscal Year The fiscal years presented are the years ended September 30, 2017 (“2017”), September 30, 2016 (“2016”), and September 30, 2015 (“2015”). Each of the Company’s first three quarters ends on the last day of the calendar month. Segment Information Operating segments are defined as components of a business that can earn revenue and incur expenses for which discrete financial information is evaluated on a regular basis by the chief operating decision maker (“CODM”) in order to decide how to allocate resources and assess performance. The Company’s CODM, the Chief Executive Officer, reviews consolidated results of operations to make decisions, therefore the Company views its operations and manages its business as one operating segment. Cash and Cash Equivalents The Company considers all highly liquid investments with maturities of three months or less when purchased to be cash equivalents. Cash and cash equivalents also include unsettled credit card transactions. Cash equivalents are comprised of money market funds which invest primarily in commercial paper or bonds with a rating of A-1 or better, and bank certificates of deposit. Accounts Receivable Accounts receivables are derived from unpaid invoiced amounts and are recorded at their net realizable value. Each month the Company reviews its receivables on a customer-by-customer basis and evaluates whether an allowance for doubtful accounts is necessary based on any known or perceived collection issues. The allowance for doubtful accounts represents the Company’s estimate of credit exposure for each customer. Any balances that are eventually deemed uncollectible are written off against the allowance after all means of collection have been exhausted and the potential for recovery is considered remote. The Company’s accounts receivable are primarily from customers in the building industry located in the United States and Canada, and no single customer represented at least 10% of the Company’s revenue during the year ended September 30, 2017, or accounts receivable as of September 30, 2017. Concentrations of Risk Financial instruments that potentially subject the Company to significant concentration of credit risk consist primarily of cash, cash equivalents and accounts receivable. The Company maintains the majority of its cash and cash equivalents with one financial institution, which management believes to be financially sound and with minimal credit risk. The Company’s deposits periodically exceed amounts guaranteed by the Federal Deposit Insurance Corporation. Inventories Inventories, consisting substantially of finished goods, are valued at the lower of cost or market (net realizable value). Cost is determined using the moving weighted-average cost method. The Company’s arrangements with vendors typically provide for rebates after it makes a special purchase and/or monthly, quarterly and/or annual rebates of a specified amount of consideration payable when a number of measures have been achieved. Annual rebates are generally related to a specified cumulative level of purchases on a calendar-year basis. The Company accounts for such rebates as a reduction of the inventory value until the product is sold, at which time such rebates reduce cost of sales in the consolidated statements of operations. Throughout the year, the Company estimates the amount of the periodic rebates based upon the expected level of purchases. The Company continually revises these estimates to reflect actual rebates earned based on actual purchase levels. Amounts due from vendors under these arrangements are included in “Prepaid expenses and other current assets” in the accompanying consolidated balance sheets. Property and Equipment Property and equipment acquired in connection with acquisitions are recorded at fair value as of the date of the acquisition and depreciated utilizing the straight-line method over the estimated remaining lives. All other additions are recorded at cost, and depreciation is computed using the straight-line method. The Company reviews the estimated useful lives of its fixed assets on an ongoing basis and the following table summarizes the estimates currently used: Asset Class Estimated Useful Life Buildings and improvements 40 years Equipment 3 to 7 years Furniture and fixtures 7 years Leasehold improvements Shorter of the estimated useful life or the term of the lease, considering renewal options expected to be exercised. Business Combinations The Company records acquisitions resulting in the consolidation of a business using the acquisition method of accounting. Under this method, the acquiring Company records the assets acquired, including intangible assets that can be identified and named, and liabilities assumed based on their estimated fair values at the date of acquisition. The purchase price in excess of the fair value of the assets acquired and liabilities assumed is recorded as goodwill. Various assumptions are used in the determination of these estimated fair values, including items such sales growth rates, cost synergies, customer attrition rates, discount rates, and other prospective financial information. Estimates associated with the accounting for acquisitions may change as additional information becomes available regarding the assets acquired and liabilities assumed. Transaction costs associated with acquisitions are expensed as incurred. Goodwill and Intangibles On an annual basis and at interim periods when circumstances require, the Company tests the recoverability of its goodwill and indefinite-lived intangible assets. Examples of such indicators include a significant change in the business climate, unexpected competition, loss of key personnel or a decline in the Company’s market capitalization below the Company’s net book value. The Company performs impairment assessments at the reporting unit level, which is defined as an operating segment or one level below an operating segment, also known as a component. The Company currently has five components which it evaluates for aggregation by examining the distribution methods, sales mix, and operating results of each component to determine if these characteristics will be sustained over a long-term basis. For purposes of this evaluation, the Company expects its components to exhibit similar economic characteristics 3-5 years after events such as an acquisition within the Company’s core roofing business or management/business restructuring. Components that exhibit similar economic characteristics are subsequently aggregated into a single reporting unit. Based on the Company’s most recent impairment assessment performed as of August 31, 2017, it was determined that all of the Company’s components exhibited similar economic characteristics, and therefore should be aggregated into a single reporting unit (collectively the “Reporting Unit”). To test for the recoverability of goodwill and indefinite-lived intangible assets, the Company first performs a qualitative assessment based on economic, industry and company-specific factors for all or selected reporting units to determine whether the existence of events and circumstances indicates that it is more likely than not that the goodwill or indefinite-lived intangible asset is impaired. Based on the results of the qualitative assessment, two additional steps in the impairment assessment may be required. The first step would require a comparison of each reporting unit’s fair value to the respective carrying value. If the carrying value exceeds the fair value, a second step is performed to measure the amount of impairment loss on a relative fair value basis, if any. Based on the Company’s most recent qualitative impairment assessment performed as of August 31, 2017, the Company concluded that there were no indicators of impairment, and that therefore it was more likely than not that the fair value of the goodwill and indefinite-lived intangible assets exceeded their net carrying amount, therefore the quantitative two-step impairment test was not required. The Company amortizes certain identifiable intangible assets that have finite lives, currently consisting of non-compete agreements, customer relationships and trade names. Non-compete agreements are amortized on a straight-line basis over the terms of the associated contractual agreements; customer relationship assets are amortized on an accelerated basis based on the expected cash flows generated by the existing customers; and trade names are amortized on an accelerated basis over a five or ten year period. Amortizable intangible assets are tested for impairment, when deemed necessary, based on undiscounted cash flows and, if impaired, are written down to fair value based on either discounted cash flows or appraised values. In connection with certain financing arrangements, the Company has debt issuance costs that are amortized over the lives of the associated financings using the effective interest method. Evaluation of Long-Lived Assets The Company evaluates the recoverability of its long-lived assets for impairment whenever events or circumstances indicate that the carrying amount of the assets may not be recoverable. Recoverability is measured by comparing the carrying amount of the asset to the future undiscounted cash flows the asset is expected to generate. If the asset is considered to be impaired, the amount of any impairment is measured as the difference between the carrying value and the fair value of the impaired asset. Fair Value Measurement The Company applies fair value accounting for all financial assets and liabilities that are reported at fair value in the financial statements on a recurring basis. Fair value is defined as the price that would be received from selling an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The accounting guidance establishes a defined three-tier hierarchy to classify and disclose the fair value of assets and liabilities on both the date of their initial measurement as well as all subsequent periods. The hierarchy prioritizes the inputs used to measure fair value by the lowest level of input that is available and significant to the fair value measurement. The three levels are described as follows: • Level 1 : Observable inputs. Quoted prices in active markets for identical assets and liabilities; • Level 2 : Observable inputs other than the quoted price. Includes quoted prices for similar instruments, quoted prices for identical or similar instruments in inactive markets and amounts derived from valuation models where all significant inputs are observable in active markets; and • Level 3 : Unobservable inputs. Includes amounts derived from valuation models where one or more significant inputs are unobservable and require the Company to develop relevant assumptions. The Company evaluates its financial assets and liabilities subject to fair value measurements on a recurring basis to determine the appropriate level of classification as of each reporting period. Financial Derivatives The Company has entered into interest rate swaps to minimize the risks and costs associated with financing activities, as well as to maintain an appropriate mix of fixed-rate and floating-rate debt. The swap agreements are contracts to exchange variable-rate for fixed-interest rate payments over the life of the agreements. The Company's derivative instruments are designated as cash flow hedges, for which the Company records the effective portions of changes in their fair value, net of tax, in other comprehensive income. The Company recognizes any ineffective portion of the hedges in the consolidated statement of operations through interest expense, financing costs and other. Net Sales The Company recognizes revenue (net sales on the consolidated statement of operations) when the following four basic criteria are met: • persuasive evidence of an arrangement exists; • delivery has occurred or services have been rendered; • the price to the buyer is fixed and determinable; and • collectability is reasonability assured. Based on these criteria, the Company generally recognizes revenue at the point of sale or upon delivery to the customer site. For goods shipped by third party carriers, the Company recognizes revenue upon shipment since the terms are generally FOB shipping point. The Company also arranges for certain products to be shipped directly from the manufacturer to the customer. The Company recognizes the gross revenue for these sales upon shipment as the terms are FOB shipping point. Leases The Company leases the majority of its facilities and enters into various other operating lease agreements in conducting its business. At the inception of each lease, the Company evaluates the lease agreement to determine whether the lease is an operating or capital lease. Operating lease expenses are recognized in the statements of operations on a straight-line basis over the term of the related lease. Some of the Company’s lease agreements may contain renewal options, tenant improvement allowances, rent holidays or rent escalation clauses. When such items are included in a lease agreement, the Company records a deferred rent asset or liability on the consolidated balance sheets equal to the difference between the rent expense and cash rent payments. The cost of property and equipment acquired under capital lease arrangements represents the lesser of the present value of the minimum lease payments or the fair value of the leased asset as of the inception of the lease. Stock-Based Compensation The Company applies the fair value method to recognize compensation expense for stock-based awards. Using this method, the estimated grant-date fair value of the award is recognized on a straight-line basis over the requisite service period based on the portion of the award that is expected to vest. The Company estimates forfeitures at the time of grant and revises the estimates, if necessary, in subsequent periods if actual forfeitures differ from those estimates. For awards with a performance-based vesting condition, the Company accrues stock-based compensation expense if it is probable that the performance condition will be achieved. Stock-based compensation expense for restricted stock units is measured based on the fair value of the Company’s common stock on the grant date. The Company utilizes the Black-Scholes option pricing model to estimate the grant-date fair value of option awards. The exercise price of option awards is set to equal the estimated fair value of the common stock at the date of the grant. The following weighted-average assumptions are also used to calculate the estimated fair value of option awards: • Expected volatility : The expected volatility of the Company’s shares is estimated using the historical stock price volatility over the most recent period commensurate with the estimated expected term of the awards. • Expected term : For employee stock option awards, the Company determines the weighted average expected term equal to the weighted period between the vesting period and the contract life of all outstanding options. • Dividend yield : The Company has not paid dividends and does not anticipate paying a cash dividend in the foreseeable future and, accordingly, uses an expected dividend yield of zero. • Risk-free interest rate : The Company bases the risk-free interest rate on the implied yield available on a U.S. Treasury note with a term equal to the estimated expected term of the awards. Foreign Currency Translation The Company’s operations located outside of the United States where the local currency is the functional currency are translated into U.S. dollars using the current rate method. Results of operations are translated at the average rate of exchange for the period. Assets and liabilities are translated at the closing rates on the period end date. Gains and losses on translation of these accounts are accumulated and reported as a separate component of equity and other comprehensive income (loss). Gains and losses on foreign currency transactions are recognized in the consolidated statements of operations as a component of interest expense, financing costs, and other. Income Taxes The Company accounts for income taxes using the liability method, which requires it to recognize a current tax liability or asset for current taxes payable or refundable and a deferred tax liability or asset for the estimated future tax effects of temporary differences between the financial statement and tax reporting bases of assets and liabilities to the extent that they are realizable. Deferred tax expense (benefit) results from the net change in deferred tax assets and liabilities during the year. FASB ASC Topic 740 prescribes a recognition threshold and measurement attribute for the financial statement recognition and measurement of a tax position taken or expected to be taken in a tax return. Based on this guidance, the Company analyzes its filing positions in all of the federal and state jurisdictions where it is required to file income tax returns, as well as all open tax years in these jurisdictions. Tax benefits from uncertain tax positions are recognized if it is more likely than not that the position is sustainable based solely on its technical merits. Net Income per Share The Company’s basic net income per share attributable to common stockholders is calculated by dividing the net income attributable to common stockholders by the weighted-average number of shares of common stock outstanding for the period. The Company’s diluted net income per share is calculated by giving effect to all potentially dilutive common stock equivalents when determining the weighted-average number of common shares outstanding. For purposes of the dilutive net income per share calculation, common shares issuable upon the exercise of stock options or release of restricted stock units are considered to be common stock equivalents. Recent Accounting Pronouncements - Adopted In August 2014, the FASB issued ASU No. 2014-15, “ Presentation of Financial Statements—Going Concern: Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern In April 2015, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2015-03, “ Simplifying the Presentation of Debt Issuance Costs In September 2015, the FASB issued ASU 2015-16, “ Simplifying the Accounting for Measurement-Period Adjustments In November 2015, the FASB issued ASU 2015-17, " Balance Sheet Classification of Deferred Taxes Recent Accounting Pronouncements - Not Yet Adopted In May 2014, the FASB issued ASU 2014-09, “ Revenue from Contracts with Customers In July 2015, the FASB issued ASU 2015-11, “ Inventory: Simplifying the Measurement of Inventory. In February 2016, the FASB issued ASU 2016-02, “ Leases In March 2016, the FASB issued ASU 2016-09, “ Compensation—Stock Compensation: Improvements to Employee Share-Based Payment Accounting.” In June 2016, the FASB issued ASU 2016-13, “ Financial Instruments – Credit Losses: Measurement of Credit Losses on Financial Instruments.” In January 2017, the FASB issued ASU 2017-01, “ Business Combinations: Clarifying the Definition of a Business.” In January 2017, the FASB issued ASU 2017-04, “ Simplifying the Accounting for Goodwill Impairment.” In May 2017, the FASB issued ASU 2017-09, “Scope of Modification Accounting.”

Acquisitions

Acquisitions	12 Months Ended
	Sep. 30, 2017
Business Combinations [Abstract]
Acquisitions	3. Acquisitions Roofing Supply Group On October 1, 2015, the Company acquired 100% of the equity of Roofing Supply Group, LLC ("RSG”), a leading roofing products distributor owned by investment firm Clayton, Dubilier & Rice ("CD&R"). RSG’s results of operations have been included with Company’s consolidated results beginning October 1, 2015. RSG distributed roofing supplies and related materials from 85 locations across 25 states as of October 1, 2015. Total consideration paid for RSG was approximately $1.17 billion, out of which $288.2 million was in cash, $306.8 million of Company’s common stock and option replacement awards, and $574.4 million in refinancing of RSG’s debt. The RSG long-term debt was repaid simultaneously with the proceeds of a new ABL Revolver, Term Loan and Senior Notes (see Note 8). In connection with the RSG Acquisition, the Company was required to issue equity awards to certain RSG employees in replacement of RSG equity awards that were cancelled at closing. The replacement awards consisted of options to purchase 661,349 shares of the Company’s common stock. The terms and fair value of these awards approximated the cancelled RSG awards on the issuance date. The fair value of the replacement awards associated with services rendered through the date of the RSG Acquisition was recognized as a component of the total acquisition consideration, and the remaining fair value of the replaced awards will be recognized as an expense on a straight-line basis over the remaining service period. The RSG Acquisition has been accounted for as a business combination in accordance with the requirements of ASC 805 Business Combinations Cash $ 16,451 Accounts receivable 177,251 Inventory 179,651 Other current assets 50,000 Property, plant, and equipment 55,159 Other intangible assets 382,600 Goodwill 617,477 Current liabilities (252,190 ) Non-current liabilities (56,949 ) Total purchase price $ 1,169,450 RSG’s future growth attributable to new customers, geographic market presence and assembled workforce are additional assets that are not separable and which contributed to recorded goodwill, of which $86.1 million is tax deductible as of the October 1, 2015 RSG acquisition date. All of the Company’s goodwill plus the indefinite-lived trade name are tested for impairment annually, and all acquired goodwill and intangible assets are subject to review for impairment should future indicators of impairment develop. The fair value of accounts receivables acquired is $177.3 million, with the gross contractual amount being $185.9 million. Net sales and net loss from the RSG Acquisition included in the Company’s statements of operations for the year ended September 30, 2016 was $1.4 billion and $10.3 million, respectively. The following table represents the unaudited pro forma consolidated revenue and net income (loss) for the Company for the prior periods indicated (in thousands, except per share amount): Year Ended September 30, 2015 (unaudited) Net sales $ 3,707,629 Net income 13,051 Net income per share 0.22 The above pro forma results have been calculated by combining the historical results of the Company and RSG as if it had occurred on October 1, 2014, and adjusting the income tax provision as if it had been calculated on the combined results. The pro forma results include an estimate for all periods for intangible asset amortization (subject to change when the final asset values have been determined), stock compensation expense, interest expense, and also reflect $58.2 million of direct acquisition costs in fiscal 2015 instead of in 2016, however they do not include the impact of any cost synergies realized as a result of the acquisition. No other material pro forma adjustments to the 2015 acquisitions were deemed necessary to conform with the Company’s accounting policies. The pro forma information is not necessarily indicative of the results that would have been achieved had the transactions occurred on October 1, 2014 or that may be achieved in the future. Additional Acquisitions – Fiscal Year 2017 During fiscal year 2017, the Company acquired 23 branches from the following five acquisitions: • On December 16, 2016, the Company purchased certain assets of BJ Supply Company, a distributor of roofing and related building products with 1 branch serving Pennsylvania and New Jersey and annual sales of approximately $4 million. • On January 3, 2017, the Company acquired American Building & Roofing, Inc., a distributor of mainly residential roofing and related building products with 7 branches around Washington State and annual sales of approximately $36 million. • On January 9, 2017, the Company acquired Eco Insulation Supply, a distributor of insulation and related accessories with 1 branch serving Connecticut, Southern New England and the New York City metropolitan area and annual sales of approximately $8 million. • On March 1, 2017, the Company acquired Acme Building Materials, Inc., a distributor of residential roofing and related building products with 3 branches in Eastern Michigan and annual sales of approximately $13 million. • On May 1, 2017, the Company purchased certain assets of Lowry’s Inc., a distributor of waterproofing and concrete restoration materials with 11 branches operating in California, Arizona, Utah and Hawaii and annual sales of approximately $76 million. The Company recorded the acquired assets and liabilities related to these transactions at their estimated fair values as of the respective acquisition dates, with resulting goodwill of $53.0 million (all of which is deductible for tax purposes) and $47.4 million in intangible assets associated with these other acquisitions. Additional Acquisitions – Fiscal Year 2016 During fiscal year 2016, the Company acquired 42 branches from the following seven additional acquisitions: • On December 1, 2015, the Company purchased certain assets of RCI Roofing Supply, a distributor of residential and commercial roofing and related products with 5 branches operating in Nebraska, Iowa and Colorado with annual sales of approximately $23 million. The Company has finalized the acquisition accounting entries for this transaction. • On December 18, 2015, the Company acquired 100% of the equity interests of Roofing and Insulation Supply, a distributor primarily of residential and commercial insulation along with roofing and related products with 20 branches spanning 13 states operating across New England, the Mid-Atlantic, the Southeast, the Upper Midwest, Texas and Colorado with annual sales of approximately $70 million. The Company has finalized the acquisition accounting entries for this transaction. • On December 29, 2015, the Company purchased certain assets of Statewide Wholesale, a distributor of residential and commercial roofing and related products with 1 branch located in Denver, Colorado with annual sales of approximately $15 million. The Company has finalized the acquisition accounting entries for this transaction. • On April 1, 2016, the Company purchased certain assets of Atlantic Building Products, a distributor of decking, windows, siding, and related products with 2 branches operating in eastern Pennsylvania with annual sales of approximately $5 million. The Company has finalized the acquisition accounting entries for this transaction. • On April 1, 2016, the Company purchased certain assets of Lyf-Tym Building Products, a distributor of siding, windows, gutters, vinyl railings, and related products with 6 branches operating in North Carolina and Virginia with annual sales of approximately $20 million. The Company has finalized the acquisition accounting entries for this transaction. • On May 2, 2016, the Company purchased certain assets of Fox Brothers Company, a distributor of roofing, siding, windows, doors, and related products with 4 branches operating in Michigan with annual sales of approximately $35 million. The Company has finalized the acquisition accounting entries for this transaction. • On June 1, 2016, the Company acquired 100% of the equity interests of Woodfeathers, Inc., a distributor of primarily residential roofing and related products with 4 branches operating in Oregon and Washington with annual sales of approximately $30 million. The Company has finalized the acquisition accounting entries for this transaction. The Company recorded the acquired assets and liabilities related to these transactions at their estimated fair values as of the respective acquisition dates, with resulting goodwill of $84.8 million ($59.8 million of which is deductible for tax purposes) and $60.8 million in intangible assets associated with these other acquisitions. The Company has not provided pro forma results of operations for any of these transactions, as they were not material to the Company on either an individual or an aggregate basis. The results of operations for each of these acquisitions are included in the Company’s respective consolidated statements of income from the date of each acquisition. Acquisitions – Additional Information For those acquisitions where the acquisition accounting entries have yet to be finalized, the Company’s allocation of the purchase price is subject to change on receipt of additional information, including, but not limited to, the finalization of asset valuations (intangible and fixed) and income tax accounting.

Net Income per Share

Net Income per Share	12 Months Ended
	Sep. 30, 2017
Earnings Per Share [Abstract]
Net Income per Share	4. Net Income per Share The following table presents the basic and diluted weighted-average shares outstanding for each period presented: Year Ended September 30, 2017 2016 2015 Weighted-average common shares outstanding, basic 60,315,648 59,424,372 49,578,130 Effect of dilutive securities: Stock options 619,732 706,780 481,039 Restricted stock units 408,883 286,915 114,309 Weighted-average common shares outstanding, diluted 61,344,263 60,418,067 50,173,478 The following table includes the number of shares that may be dilutive common shares in the future. These shares were not included in the computation of diluted net income per share because the effect was either anti-dilutive or the requisite performance conditions were not met: Year Ended September 30, 2017 2016 2015 Stock options 331,681 502,294 1,313,689 Restricted stock units 61,890 45,220 -

Prepaid Expenses and Other Curr

Prepaid Expenses and Other Current Assets	12 Months Ended
	Sep. 30, 2017
Prepaid Expenses And Other Current Assets [Abstract]
Prepaid Expenses and Other Current Assets	5. Prepaid Expenses and Other Current Assets The following table summarizes the significant components of prepaid expenses and other current assets (in thousands): September 30, 2017 2016 Vendor rebates $ 193,071 $ 149,052 Other 16,067 14,051 $ 209,138 $ 163,103

Property and Equipment

Property and Equipment	12 Months Ended
	Sep. 30, 2017
Property Plant And Equipment [Abstract]
Property and Equipment	6. Property and Equipment The following table provides a detailed breakout of property and equipment, by type (in thousands): September 30, 2017 2016 Land $ 2,796 $ 2,925 Buildings and leasehold improvements 38,995 35,754 Equipment 293,489 263,947 Furniture and fixtures 23,140 20,155 Total property and equipment 358,420 322,781 Less: accumulated depreciation and amortization (202,291 ) (174,212 ) Total property and equipment, net $ 156,129 $ 148,569 Depreciation expense for the years ending September 30, 2017, 2016, and 2015 was $34.0 million, $31.9 million, and $18.7 million, respectively.

Goodwill and Intangibles

Goodwill and Intangibles	12 Months Ended
	Sep. 30, 2017
Goodwill And Intangible Assets Disclosure [Abstract]
Goodwill and Intangibles	7. Goodwill and Intangibles Goodwill The following table sets forth the change in the carrying amount of goodwill for the Company during the years ended September 30, 2017 and 2016 (in thousands): Balance at September 30, 2015 $ 496,415 Acquisition of RSG 617,477 Other acquisitions 84,853 Translation and other adjustments (1,180 ) Balance at September 30, 2016 $ 1,197,565 Acquisitions 53,012 Translation and other adjustments 1,409 Balance at September 30, 2017 $ 1,251,986 The change in the carrying amount of goodwill for the year ended September 30, 2017 and 2016 is primarily attributable to the Company’s acquisitions finalized during the respective periods presented (see Note 3). The Company has recognized no goodwill impairments for any of the periods presented. Intangible Assets In connection with transactions finalized for the year ended September 30, 2017, the Company recorded intangible assets of $47.4 million ($42.7 million of customer relationships, $4.6 million of amortizable trademarks and $0.1 million of beneficial lease arrangements). Intangible assets consisted of the following (in thousands, except time period amounts): September 30, Weighted- Average Remaining Life 1 2017 2016 (Years) Amortizable intangible assets: Non-compete agreements $ 2,824 $ 3,324 3.31 Customer relationships 610,026 566,964 17.61 Trademarks 10,500 5,400 8.37 Beneficial lease arrangements 1,060 960 8.79 Total amortizable intangible assets 624,410 576,648 Less: Accumulated amortization (268,391 ) (185,674 ) Total amortizable intangible assets, net $ 356,019 $ 390,974 Indefinite lived trademarks 73,050 73,050 Total intangibles, net $ 429,069 $ 464,024 1 For the years ended September 30, 2017, 2016, and 2015, the Company recorded $82.5 million, $68.3 million, and $16.2 million of amortization expense relating to the above-listed intangible assets, respectively. The intangible asset lives range from 5 to 20 years and the weighted-average remaining life was 17.4 years as of September 30, 2017. The following table presents the estimated annual amortization expense for these intangible assets (in thousands): Year Ending September 30, 2018 $ 71,577 2019 58,771 2020 47,751 2021 38,248 2022 30,239 Thereafter 109,433 $ 356,019

Financing Arrangements

Financing Arrangements	12 Months Ended
	Sep. 30, 2017
Debt Disclosure [Abstract]
Financing Arrangements	8. Financing Arrangements In connection with the RSG Acquisition on October 1, 2015, the Company entered into various financing arrangements totaling $1.45 billion. A “Senior Secured Credit Facility” was entered into that is comprised of an asset-based revolving line of credit (“ABL”) of $700.0 million ($350.0 million of which was drawn at closing) and a new $450.0 million term loan (“Term Loan”). The Company also raised an additional $300.0 million through the issuance of senior notes (the “Senior Notes”). The proceeds from the Senior Secured Credit Facility and Senior Notes were used to provide working capital and funds for other general corporate purposes, to refinance or otherwise extinguish all third-party indebtedness for borrowed money under Company’s and RSG’s existing senior secured credit facilities and RSG’s unsecured senior notes due 2020, to finance the acquisition, and to pay fees and expenses associated with the RSG acquisition. The Company incurred financing costs totaling approximately $31.3 million. The following table summarizes all financing arrangements the Company has entered into (in thousands): September 30, September 30, 2017 2016 Senior Secured Credit Facility Revolving Lines of Credit: U.S. Revolver, expires October 1, 2020 1 $ - $ 355,087 Canadian Revolver, expires October 1, 2020 2 3,205 4,574 Term Loan, matures October 1, 2022 3 433,440 436,380 Total borrowings under Senior Secured Credit Facility 436,645 796,041 Less: current portion (4,500 ) (4,500 ) Total long-term borrowings under Senior Secured Credit Facility $ 432,145 $ 791,541 Senior Notes Senior Notes, matures October 2023 4 292,328 291,049 Less: current portion - - Total long-term borrowings under Senior Notes $ 292,328 $ 291,049 Equipment Financing Facilities and Other Equipment financing facilities, various maturities through September 2021 5 $ 15,445 $ 20,419 Capital lease obligations, various maturities through November 2021 6 19,956 25,013 Total obligations under equipment financing facilities and other 35,401 45,432 Less: current portion (9,641 ) (10,311 ) Total long-term obligations under equipment financing facilities and other $ 25,760 $ 35,121 1 2 3 4 5 6 Asset-based Line of Credit (“ABL”) On October 1, 2015, the Company entered into a $700 million ABL with Wells Fargo Bank, N.A. and a syndicate of other lenders. This ABL consists of revolving loans in both the United States (“U.S. Revolver”) in the amount of $670 million and Canada (“Canada Revolver”) in the amount of $30 million. The ABL has a maturity date of October 1, 2020. The ABL has various borrowing tranches with an interest rate of LIBOR plus a margin of 125 basis points, 150 basis points or 175 basis points, based on the total outstanding balance of each tranche. The LIBOR rates can be fixed at one, three, six, or twelve month intervals and any non-fixed LIBOR amounts revert to a 4.75% base rate. There is one financial covenant under the ABL, which is a Consolidated Fixed Charge Ratio. The Consolidated Fixed Charge Ratio is calculated by dividing consolidated earnings before interest, taxes, depreciation and amortization (EBITDA) by Consolidated Fixed Charges (as defined in the agreement). Per the covenant, the Company’s Consolidated Fixed Charge Ratio must be a minimum of 1.00 at the end of each fiscal quarter, calculated on a trailing four quarter basis. The covenant is only applicable when the borrowing availability is less than 10% of the maximum loan cap or $60.0 million. The ABL is guaranteed jointly and severally and fully and unconditionally by the Company’s active United States subsidiary. Term Loan On October 1, 2015, the Company entered into a $450.0 million Term Loan with Citibank N.A., and a syndicate of other lenders. The Term Loan requires quarterly principal payments in the amount of $1.1 million, with the remaining outstanding principal to be paid on its maturity date of October 1, 2022. The interest rate paid is based on a LIBOR rate (with a floor) plus a fixed spread. The Company has the option of selecting a LIBOR period that determines the rate at which interest can accrue on the Term Loan as well as the period in which interest payments are made. On September 16, 2016, the Company refinanced its Term Loan, lowering the LIBOR floor by 25 basis points and lowering the spread by 25 basis points. As a result of the refinancing, the Company wrote off $1.6 million of debt issuance costs in interest expense. As of September 30, 2017, the outstanding balance on the Term Loan, net of debt issuance fees, was $433.4 million. The Term Loan is guaranteed jointly and severally and fully and unconditionally by the Company’s active United States subsidiary. Senior Notes On October 1, 2015, the Company raised $300.0 million by issuing senior notes due 2023 (the “Senior Notes”). The Senior Notes have a coupon rate of 6.38% per annum and are payable semi-annually in arrears beginning April 1, 2016. There are early payment provisions in the Senior Note indenture in which the Company would be subject to “make whole” provisions. Management anticipates repaying the notes at the maturity date of October 1, 2023. As of September 30, 2017 the outstanding balance on the Senior Notes, net of debt issuance fees, was $292.3 million. The Senior Notes are guaranteed jointly and severally and fully and unconditionally by the Company’s active United States subsidiary. Other Information The Senior Secured Credit Facility and the previous credit facility it replaced had certain lenders who participated in both arrangements, therefore management accounted for a portion of this transaction as a debt modification and a portion as a debt extinguishment. In accordance with the accounting for debt modification, the Company expensed $2.2 million of direct issuance costs incurred and will amortize the previously capitalized issuance costs over the term of the Senior Secured Credit Facility. The remainder of the settlement of the Company’s previous financing arrangements was accounted for as debt extinguishment, for which the Company recognized a loss of $0.8 million in the first quarter of fiscal year 2016. Annual principal payments for all outstanding financing arrangements for each of the next five years and thereafter are as follows (in thousands): Year Ending September 30, ABL Term Loan Senior Notes Equipment Financing Facilities Total 2018 $ - $ 4,500 $ - $ 9,584 $ 14,084 2019 - 4,500 - 9,631 14,131 2020 3,205 4,500 - 8,960 16,665 2021 - 4,500 - 4,367 8,867 2022 - 4,500 - 172 4,672 Thereafter - 418,500 300,000 141 718,641 Total debt 3,205 441,000 300,000 32,855 777,060 Less: Unamortized debt issuance costs 1 - (7,560 ) (7,672 ) - (15,232 ) Total long-term debt $ 3,205 $ 433,440 $ 292,328 $ 32,855 $ 761,828 1 Equipment Financing Facilities and Other As of September 30, 2017, the Company had a $15.4 million outstanding under equipment financing facilities, with fixed interest rates ranging from 2.33% to 3.25% and payments due through September 2021. As of September 30, 2017, the Company had $20.0 million of capital lease obligations outstanding. These leases have interest rates ranging from 2.72% to 10.39% with payments due through November 2021.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Sep. 30, 2017
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	9. Commitments and Contingencies Operating Leases The Company mostly operates in leased facilities, which are accounted for as operating leases. The leases typically provide for a base rent plus real estate taxes. Certain of the leases provide for escalating rents over the lives of the leases and rent expense is recognized over the terms of those leases on a straight-line basis. At September 30, 2017, the minimum rental commitments under all non-cancelable operating leases with initial or remaining terms of more than one year were as follows: Year Ending September 30, Operating Leases 2018 $ 57,075 2019 46,177 2020 37,199 2021 30,350 2022 23,496 Thereafter 29,257 Total minimum lease payments $ 223,554 Rent expense was $60.1 million, $59.3 million, and $39.2 million for the years ending September 30, 2017, 2016, and 2015, respectively. Sublet income was immaterial for each of these periods. Contingencies The Company is subject to loss contingencies pursuant to various federal, state and local environmental laws and regulations; however, the Company is not aware of any reasonably possible losses that would have a material impact on its results of operations, financial position, or liquidity. Potential loss contingencies include possible obligations to remove or mitigate the effects on the environment of the placement, storage, disposal or release of certain chemical or other substances by the Company or by other parties. In connection with its acquisitions, the Company’s practice is to request indemnification for any and all known material liabilities of significance as of the respective dates of acquisition. Historically, environmental liabilities have not had a material impact on the Company's results of operations, financial position or liquidity. The Company is subject to litigation from time to time in the ordinary course of business; however the Company does not expect the results, if any, to have a material adverse impact on its results of operations, financial position or liquidity.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Sep. 30, 2017
Equity [Abstract]
Stockholders' Equity	10. Stockholders’ Equity Common and Preferred Stock The Company is authorized to issue 100 million shares of common stock and 5 million shares of preferred stock. As of September 30, 2017 and 2016 there were 67,700,858 and 59,890,885 shares of common stock issued and outstanding, respectively, and no preferred stock outstanding as of either period end. On September 25, 2017, in connection with the Allied Acquisition (see “Subsequent Events” footnote), the Company issued 7,273,750 shares of its common stock in a secondary offering at a price of $47.50 per share. Total net proceeds from this secondary offering were $330.8 million. Accumulated Other Comprehensive Income (Loss ) Other comprehensive income (loss) is comprised of certain gains and losses that are excluded from net income under GAAP and instead recorded as a separate element of stockholders’ equity. The Company’s other comprehensive income (loss) consists of foreign currency translation adjustments as well as unrealized gains or losses on the Company’s derivative contracts. The following table summarizes the components of accumulated other comprehensive loss (in thousands): Foreign Currency Translation Derivative Financial Instruments Accumulated Other Comprehensive Loss Balance as of September 30, 2014 $ (2,040 ) $ (4,539 ) $ (6,579 ) Other comprehensive loss before reclassifications (14,003 ) (138 ) (14,141 ) Reclassifications out of other comprehensive loss - - - Balance as of September 30, 2015 $ (19,293 ) $ (1,427 ) $ (20,720 ) Other comprehensive income before reclassifications 1,024 - 1,024 Reclassifications out of other comprehensive loss - 1,039 1,039 Balance as of September 30, 2016 $ (18,269 ) $ (388 ) $ (18,657 ) Other comprehensive income before reclassifications 3,706 - 3,706 Reclassifications out of other comprehensive loss - 388 388 Balance as of September 30, 2017 $ (14,563 ) $ - $ (14,563 ) Gains (losses) on derivative instruments are recognized in the consolidated statements of operations in interest expense, financing costs, and other.

Stock-based Compensation

Stock-based Compensation	12 Months Ended
	Sep. 30, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-based Compensation	11. Stock-based Compensation On February 9, 2016, the shareholders of the Company approved the Amended and Restated Beacon Roofing Supply, Inc. 2014 Stock Plan (the “2014 Plan”). The 2014 Plan provides for discretionary awards of stock options, stock awards, restricted stock units, and stock appreciation rights (“SARs”) for up to 5,000,000 shares of common stock to selected employees and non-employee directors. The 2014 Plan mandates that all forfeited, expired, and withheld shares, including those from the predecessor plans, be returned to the 2014 Plan and made available for issuance. As of September 30, 2017, there were 4,096,732 shares of common stock available for issuance. Prior to the 2014 Plan, the Company maintained the amended and restated Beacon Roofing Supply, Inc. 2004 Stock Plan (the “2004 Plan”). Upon shareholder approval of the 2014 Plan, the Company ceased issuing equity awards from the 2004 Plan and mandated that all future equity awards will be issued from the 2014 Plan. For all equity awards granted prior to October 1, 2014, in the event of a change in control of the Company, all awards are immediately vested. Beginning in fiscal 2015, equity awards contain a “double trigger” change in control mechanism. Unless an award is continued or assumed by a public company in an equitable manner, an award shall become fully vested immediately prior to a change in control (at 100% in the case of a performance-based restricted stock award). If an award is so continued or assumed, vesting will continue in accordance with the terms of the award, unless there is a qualifying termination within one-year following the change in control, in which event the award shall become fully vested immediately (at 100% in the case of a performance-based restricted stock award). Stock Options Non-qualified stock options generally expire 10 years after the grant date and, except under certain conditions, the options are subject to continued employment and vest in one-third increments over a three-year period following the grant dates. The fair values of the options granted for the year ended September 30, 2017 were estimated on the dates of grants using the Black-Scholes option-pricing model with the following weighted-average assumptions: Year Ended September 30, 2017 2016 2015 Risk-free interest rate 1.97 % 1.87 % 1.83 % Expected volatility 28.83 % 30.96 % 31.69 % Expected life (in years) 5.30 5.6 5.6 Dividend yield — — — The following table summarizes all stock option activity for the periods presented (in thousands, except share, per share, and time period amounts): Options Outstanding Weighted- Average Exercise Price Weighted- Average Remaining Contractual Term (Years) Aggregate Intrinsic Value 1 Balance as of September 30, 2016 2,312,789 $ 25.55 6.3 $ 38,225 Granted 245,818 47.40 Exercised (442,909 ) 22.09 Canceled/Forfeited (16,992 ) 33.72 Expired (14,478 ) 19.50 Balance as of September 30, 2017 2,084,228 $ 28.84 6.1 $ 46,714 Vested and expected to vest after September 30, 2017 2,050,134 $ 28.74 6.0 $ 46,150 Exercisable as of September 30, 2017 1,414,141 $ 25.06 5.0 $ 37,033 1 Aggregate intrinsic value as represents the difference between the closing fair value of the underlying common stock and the exercise price of outstanding, in-the-money options on the date of measurement. During the years ended September 30, 2017 and 2016, the Company recorded stock-based compensation expense related to stock options of $4.8 million and $11.2 million, respectively. As of September 30, 2017, there was $4.7 million of total unrecognized compensation cost related to unvested stock options, which is expected to be recognized over a weighted-average period of 1.8 years. The following table summarizes additional information on stock options for the period presented (in thousands): Year Ended September 30, 2017 2016 2015 Weighted-average fair value of stock options granted $ 14.21 $ 12.89 $ 9.40 Total fair value of stock options vested 5,566 12,347 6,399 Total intrinsic value of stock options exercised 10,941 22,693 4,615 Restricted Stock Units Restricted stock unit (“RSU”) awards granted to employees are subject to continued employment and generally vest after three years. The Company also grants certain RSU awards to management that contain an additional vesting condition tied directly to a defined performance metric for the Company. The actual number of RSUs that will vest can range from 0% to 150% of the grant, depending upon actual Company performance below or above the target level. The Company estimates performance in relation to the established target when determining the projected number of RSUs that will vest and calculating the compensation cost related to these awards. RSUs granted to non-employee directors are subject to continued service and vest after one year (except under certain conditions). Generally, the common shares underlying the RSUs are not eligible for distribution until the director’s service on the Board has terminated. For non-employee director RSU grants made prior to fiscal year 2014, the share distribution date is six months after the director’s termination of service on the board. RSU grants made in fiscal year 2014 and thereafter have no such holding period requirement. Additionally, beginning in fiscal year 2016 non-employee directors holding common stock and outstanding vested unexercised/unsettled equity awards with a fair value that is greater than or equal to five times the annual cash retainer may elect to have future grants settle simultaneously with vesting. The following table summarizes all restricted stock unit activity for the periods presented: RSUs Outstanding Weighted-Average Grant Date Fair Value Balance at September 30, 2016 705,434 $ 34.55 Granted 273,065 47.31 Released (128,578 ) 33.47 Canceled/Forfeited (78,948 ) 29.04 Balance at September 30, 2017 770,973 $ 38.95 Vested and expected to vest after September 30, 2017 793,350 $ 38.88 During the years ended September 30, 2017 and 2016, the Company recorded stock-based compensation expense related to restricted stock units of $10.3 million and $6.5 million, respectively. As of September 30, 2017, there was $12.9 million of total unrecognized compensation cost related to unvested restricted stock units, which is expected to be recognized over a weighted-average period of 1.8 years. The following table summarizes additional information on RSUs for the period presented (in thousands): Year Ended September 30, 2017 2016 2015 Weighted-average fair value of RSUs granted $ 47.31 $ 38.92 $ 28.74 Total fair value of RSUs vested 4,562 743 1,943 Total intrinsic value of RSUs released 6,079 1,375 1,784

Income Taxes

Income Taxes	12 Months Ended
	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Income Taxes	12. Income Taxes The following table summarizes the components of the income tax provision (in thousands): Year Ended September 30, 2017 2016 2015 Current: Federal $ 52,718 $ 23,403 $ 17,414 Foreign 1,366 1,183 1,765 State 8,975 2,426 7,579 Total current taxes $ 63,059 $ 27,012 $ 26,758 Deferred: Federal $ (656 ) $ 25,935 $ 14,798 Foreign - 321 (657 ) State 78 3,347 2,868 Total deferred taxes $ (578 ) $ 29,603 $ 17,009 Provision for income taxes $ 62,481 $ 56,615 $ 43,767 The following table is a reconciliation of the statutory federal income tax rate to the Company’s effective income tax rate for the periods presented: Year Ended September 30, 2017 2016 2015 U.S. federal income taxes at statutory rate 35.0 % 35.0 % 35.0 % State income taxes, net of federal benefit 3.9 % 4.2 % 4.6 % Non-deductible professional fees related to RSG acquisition 0.0 % 0.4 % 2.2 % Other (0.6 %) (1.0 %) (0.5 %) Effective tax rate 38.3 % 38.6 % 41.3 % Deferred income taxes reflect the tax consequences of temporary differences between the amounts of assets and liabilities for financial reporting purposes and such amounts as measured by tax law. These temporary differences are determined according to ASC 740 Income Taxes. Temporary differences that give rise to deferred tax assets and liabilities are as follows (in thousands): September 30, 2017 2016 Deferred tax assets: Deferred compensation $ 14,237 $ 15,166 Allowance for doubtful accounts 1,318 2,060 Accrued vacation and other 6,602 6,616 Unrealized loss on financial derivatives - 279 Inventory valuation 10,564 6,193 Tax loss carryforwards 20,575 34,505 Other 958 913 Total deferred tax assets $ 54,254 $ 65,732 Deferred tax liabilities: Excess tax over book depreciation and amortization $ (192,637 ) $ (201,214 ) Total deferred tax liabilities (192,637 ) (201,214 ) Net deferred income tax liabilities $ (138,383 ) $ (135,482 ) Due to the RSG acquisition on October 1, 2015, the Company acquired $135.3 million of federal and state net operating loss (“NOL”) carryforwards related to its domestic operations. The federal losses are subject to an annual Section 382 limit of $37.3 million. The Company utilized $37.3 million of federal NOLs and $2.3 million of state NOLs for the year ended September 30, 2017. These NOLs are scheduled to expire at various dates through 2035. The deferred tax asset of $20.6 million remaining as of September 30, 2017 is related to the federal and state NOL carryforward and AMT credit carryforward. The Company’s Canadian subsidiary, Beacon Roofing Supply Canada Company (“BRSCC”), is treated as a Controlled Foreign Corporation (“CFC”). BRSCC’s taxable income, which reflects all of the Company’s Canadian operations, is being taxed only in Canada and would generally be taxed in the United States only upon an actual or deemed distribution. The Company expects that BRSCC’s earnings will be indefinitely reinvested for the foreseeable future and therefore no United States deferred tax asset or liability for the differences between the book basis and the tax basis of BRSCC has been recorded at September 30, 2017. Unremitted earnings of $44.5 million were considered permanently reinvested at September 30, 2017. Of this amount, $22.4 million of the unremitted earnings were previously taxed in the United States and the remittance on these earnings would not generate additional United States tax. As of September 30, 2017, goodwill was $1.25 billion, of which there remains an amortizable basis of $297.4 million for income tax purposes. The Company had $34.5 million of excess tax benefits available for potential deferred tax write-offs as of September 30, 2017, primarily related to previously recognized stock-based compensation. As of September 30, 2017, there were no uncertain tax positions which, if recognized, would affect the Company’s effective tax rate. The Company’s accounting policy is to recognize any interest and penalties related to income tax matters in income tax expense in the consolidated statements of operations. A reconciliation of the beginning and ending amounts of the gross unrecognized income tax benefits is as follows: Year Ended September 30, 2017 2016 Balance, beginning of year $ - $ 82 Current year uncertain tax positions - - Settlements - (82 ) Balance, end of year $ - $ - The Company has operations in 48 U.S. states and 6 provinces in Canada. The Company is currently under audit in certain state and local jurisdictions for various years. These audits may involve complex issues, which may require an extended period of time to resolve. The Company has provided for its estimate of taxes payable in the accompanying financial statements. Additional taxes are reasonably possible; however the amounts cannot be estimated at this time. The Company is no longer subject to U.S. federal income tax examinations for any fiscal years ended on or before September 30, 2013. For the majority of states, the Company is also no longer subject to tax examinations for any fiscal years ended on or before September 30, 2013. In Canada, the Company is no longer subject to tax examinations for any fiscal years ended on or before September 30, 2013. For the Canadian provinces, the Company is no longer subject to tax examinations for any fiscal years ended on or before September 30, 2014.

Geographic and Product Data

Geographic and Product Data	12 Months Ended
	Sep. 30, 2017
Segment Reporting [Abstract]
Geographic and Product Data	13. Geographic and Product Data The following tables summarize certain geographic information for the periods presented (in thousands): Year Ended September 30, 2017 2016 2015 Net sales U.S. $ 4,198,935 $ 3,949,067 $ 2,331,360 Canada 177,735 178,042 183,809 Total net sales $ 4,376,670 $ 4,127,109 $ 2,515,169 September 30, 2017 2016 Long-lived assets U.S. $ 507,236 $ 527,680 Canada 13,446 13,374 Total long-lived assets $ 520,682 $ 541,054 The following table summarizes net sales from external customers by product group (in thousands): Year Ended September 30, 2017 2016 2015 Residential roofing products $ 2,380,435 $ 2,190,762 $ 1,236,397 Non-residential roofing products 1,273,153 1,331,319 882,970 Complementary building products 723,082 605,028 395,802 Total net sales $ 4,376,670 $ 4,127,109 $ 2,515,169

Supplemental Guarantor Informat

Supplemental Guarantor Information	12 Months Ended
	Sep. 30, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Supplemental Guarantor Information	14. All of the Senior Notes issued on October 1, 2015 are guaranteed jointly and severally by all of the United States subsidiaries of the Company (collectively, the “Guarantor”), and not by the Canadian subsidiaries of the Company. Such guarantees are full and unconditional. Supplemental condensed consolidating financial information of the Company, including such information for the Guarantor, is presented below. The information is presented in accordance with the requirements of Rule 3-10 under the SEC’s Regulation S-X. The financial information may not necessarily be indicative of results of operations, cash flows or financial position had the non-guarantor subsidiaries operated as independent entities. Investments in subsidiaries are presented using the equity method of accounting. The principal elimination entries eliminate investments in subsidiaries and intercompany balances and transactions. Separate financial statements of the Guarantor are not provided as the consolidating financial information contained herein provides a more meaningful disclosure to allow investors to determine the nature of the assets held by, and the operations of, the combined groups. BEACON ROOFING SUPPLY, INC. Condensed Consolidating Balance Sheets (Unaudited; In thousands) September 30, 2017 Parent Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations and Other Consolidated Assets Current assets: Cash and cash equivalents $ - $ 149,799 $ 1,582 $ (13,131 ) $ 138,250 Accounts receivable, net - 663,034 42,633 (1,140 ) 704,527 Inventories, net - 527,226 24,698 - 551,924 Prepaid expenses and other current assets 4,195 198,817 6,126 - 209,138 Total current assets 4,195 1,538,876 75,039 (14,271 ) 1,603,839 Intercompany receivable, net - 655,372 - (655,372 ) - Investments in consolidated subsidiaries 3,160,273 - - (3,160,273 ) - Deferred income taxes, net 30,822 - - (30,822 ) - Property and equipment, net 6,610 138,955 10,564 - 156,129 Goodwill - 1,220,812 31,174 - 1,251,986 Intangibles, net - 426,187 2,882 - 429,069 Other assets, net 2,912 5,622 - - 8,534 Total Assets $ 3,204,812 $ 3,985,824 $ 119,659 $ (3,860,738 ) $ 3,449,557 Liabilities and Stockholders' Equity Current liabilities: Accounts payable $ 27,174 $ 468,891 $ 21,903 $ (14,271 ) $ 503,697 Accrued expenses 51,183 204,173 5,941 - 261,297 Current portions of long-term debt 4,500 9,641 - - 14,141 Total current liabilities 82,857 682,705 27,844 (14,271 ) 779,135 Intercompany payable, net 618,881 - 36,491 (655,372 ) - Borrowings under revolving lines of credit, net - - 3,205 - 3,205 Long-term debt, net 721,268 - - - 721,268 Deferred income taxes, net - 168,209 996 (30,822 ) 138,383 Long-term obligations under equipment financing and other, net - 25,694 66 - 25,760 Total liabilities 1,423,006 876,608 68,602 (700,465 ) 1,667,751 Total stockholders' equity 1,781,806 3,109,216 51,057 (3,160,273 ) 1,781,806 Total Liabilities and Stockholders' Equity $ 3,204,812 $ 3,985,824 $ 119,659 $ (3,860,738 ) $ 3,449,557 BEACON ROOFING SUPPLY, INC. Condensed Consolidating Balance Sheets (Unaudited; In thousands) September 30, 2016 Parent Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations and Other Consolidated Assets Current assets: Cash and cash equivalents $ - $ 37,447 $ 2,876 $ (8,937 ) $ 31,386 Accounts receivable, net - 593,395 34,710 (1,140 ) 626,965 Inventories, net - 460,516 20,220 - 480,736 Prepaid expenses and other current assets 3,527 153,681 5,895 - 163,103 Total current assets 3,527 1,245,039 63,701 (10,077 ) 1,302,190 Intercompany receivable, net - 878,931 - (878,931 ) - Investments in consolidated subsidiaries 2,891,677 - - (2,891,677 ) - Deferred income taxes, net 59,567 - - (59,567 ) - Property and equipment, net 4,626 133,897 10,046 - 148,569 Goodwill - 1,167,905 29,660 - 1,197,565 Intangibles, net - 460,696 3,328 - 464,024 Other assets, net 1,242 269 - - 1,511 Total Assets $ 2,960,639 $ 3,886,737 $ 106,735 $ (3,840,252 ) $ 3,113,859 Liabilities and Stockholders' Equity Current liabilities: Accounts payable $ 26,630 $ 329,895 $ 14,467 $ (10,077 ) $ 360,915 Accrued expenses 42,594 114,016 4,503 - 161,113 Current portions of long-term obligations 4,500 10,311 - - 14,811 Total current liabilities 73,724 454,222 18,970 (10,077 ) 536,839 Intercompany payable, net 840,159 - 38,772 (878,931 ) - Borrowings under revolving lines of credit, net - 355,087 4,574 - 359,661 Long-term debt, net 722,929 - - - 722,929 Deferred income taxes, net - 194,556 493 (59,567 ) 135,482 Long-term obligations under equipment financing and other, net - 35,074 47 - 35,121 Total liabilities 1,636,812 1,038,939 62,856 (948,575 ) 1,790,032 Total stockholders' equity 1,323,827 2,847,798 43,879 (2,891,677 ) 1,323,827 Total Liabilities and Stockholders' Equity $ 2,960,639 $ 3,886,737 $ 106,735 $ (3,840,252 ) $ 3,113,859 BEACON ROOFING SUPPLY, INC. Condensed Consolidating Statements of Operations (Unaudited; In thousands, except share and per share amounts) Year Ended September 30, 2017 Parent Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations and Other Consolidated Net sales $ - $ 4,198,935 $ 177,735 $ - $ 4,376,670 Cost of products sold - 3,162,896 137,835 - 3,300,731 Gross profit - 1,036,039 39,900 - 1,075,939 Operating expense 28,496 798,328 33,019 - 859,843 Intercompany charges (income) (4,664 ) 4,342 322 - - Income (loss) from operations (23,832 ) 233,369 6,559 - 216,096 Interest expense, financing costs, and other 38,660 14,033 58 - 52,751 Intercompany interest expense (income) (24,458 ) 22,927 1,531 - - Income (loss) before provision for income taxes (38,034 ) 196,409 4,970 - 163,345 Provision for (benefit from) income taxes (3,284 ) 64,399 1,366 - 62,481 Income (loss) before equity in net income of subsidiaries (34,750 ) 132,010 3,604 - 100,864 Equity in net income of subsidiaries 135,614 - - (135,614 ) - Net income $ 100,864 $ 132,010 $ 3,604 $ (135,614 ) $ 100,864 Weighted-average common stock outstanding: Basic 60,315,648 Diluted 61,344,263 Net income per share: Basic $ 1.67 Diluted $ 1.64 BEACON ROOFING SUPPLY, INC. Condensed Consolidating Statements of Operations (Unaudited; In thousands, except share and per share amounts) Year Ended September 30, 2016 Parent Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations and Other Consolidated Net sales $ - $ 3,949,313 $ 178,042 $ (246 ) $ 4,127,109 Cost of products sold - 2,977,174 137,112 (246 ) 3,114,040 Gross profit - 972,139 40,930 - 1,013,069 Operating expenses 59,949 715,669 32,467 - 808,085 Intercompany charges (income) (51,942 ) 49,285 2,657 - - Income (loss) from operations (8,007 ) 207,185 5,806 - 204,984 Interest expense, financing costs, and other 42,835 14,965 652 - 58,452 Intercompany interest expense (income) (21,536 ) 19,928 1,608 - - Income (loss) before provision for income taxes (29,306 ) 172,292 3,546 - 146,532 Provision for (benefit from) income taxes (472 ) 55,613 1,474 - 56,615 Income (loss) before equity in net income of subsidiaries (28,834 ) 116,679 2,072 - 89,917 Equity in net income of subsidiaries 118,751 - - (118,751 ) - Net income $ 89,917 $ 116,679 $ 2,072 $ (118,751 ) $ 89,917 Weighted-average common stock outstanding: Basic 59,424,372 Diluted 60,418,067 Net income per share: Basic $ 1.51 Diluted $ 1.49 BEACON ROOFING SUPPLY, INC. Condensed Consolidating Statements of Operations (Unaudited; In thousands, except share and per share amounts) Year Ended September 30, 2015 Parent Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations and Other Consolidated Net sales $ - $ 2,331,829 $ 183,809 $ (469 ) $ 2,515,169 Cost of products sold - 1,778,196 142,077 (469 ) 1,919,804 Gross profit - 553,633 41,732 - 595,365 Operating expenses 44,937 399,901 33,446 - 478,284 Intercompany charges (income) (36,085 ) 34,264 1,821 - - Income (loss) from operations (8,852 ) 119,468 6,465 - 117,081 Interest expense, financing costs, and other 9,508 740 789 - 11,037 Intercompany interest expense (income) (15,762 ) 14,174 1,588 - - Income before provision for income taxes (2,598 ) 104,554 4,088 - 106,044 Provision for income taxes (1,087 ) 43,765 1,089 - 43,767 Income before equity in net income of subsidiaries (1,511 ) 60,789 2,999 - 62,277 Equity in net income of subsidiaries 63,788 - - (63,788 ) - Net income $ 62,277 $ 60,789 $ 2,999 $ (63,788 ) $ 62,277 Weighted-average common stock outstanding: Basic 49,578,130 Diluted 50,173,478 Net income per share: Basic $ 1.26 Diluted $ 1.24 BEACON ROOFING SUPPLY, INC. Condensed Consolidating Statements of Comprehensive Income (Unaudited; In thousands) Year Ended September 30, 2017 Parent Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations and Other Consolidated Net income (loss) $ 100,864 $ 132,010 $ 3,604 $ (135,614 ) $ 100,864 Other comprehensive income: Foreign currency translation adjustment 3,706 - 3,706 (3,706 ) 3,706 Total other comprehensive income 3,706 - 3,706 (3,706 ) 3,706 Comprehensive income (loss) $ 104,570 $ 132,010 $ 7,310 $ (139,320 ) $ 104,570 Year Ended September 30, 2016 Parent Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations and Other Consolidated Net income $ 89,917 $ 116,679 $ 2,072 $ (118,751 ) $ 89,917 Other comprehensive income: Foreign currency translation adjustment 1,024 - 1,024 (1,024 ) 1,024 Total other comprehensive income 1,024 - 1,024 (1,024 ) 1,024 Comprehensive income $ 90,941 $ 116,679 $ 3,096 $ (119,775 ) $ 90,941 Year Ended September 30, 2015 Parent Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations and Other Consolidated Net income $ 62,277 $ 60,789 $ 2,999 $ (63,788 ) $ 62,277 Other comprehensive income (loss): Foreign currency translation adjustment (14,003 ) - (14,003 ) 14,003 (14,003 ) Unrealized loss due to change in fair value of derivatives, net of tax (138 ) - - - (138 ) Total other comprehensive income (loss) (14,141 ) - (14,003 ) 14,003 (14,141 ) Comprehensive income (loss) $ 48,136 $ 60,789 $ (11,004 ) $ (49,785 ) $ 48,136 BEACON ROOFING SUPPLY, INC. Condensed Consolidating Statements of Cash Flows (Unaudited; In thousands) Year Ended September 30, 2017 Parent Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations and Other Consolidated Net cash provided by (used in) operating activities $ (2,466 ) $ 313,396 $ 4,888 $ (618 ) $ 315,200 Investing Activities Purchases of property and equipment (3,517 ) (34,584 ) (1,727 ) - (39,828 ) Acquisition of businesses (129,390 ) - - - (129,390 ) Proceeds from the sale of assets - 2,150 83 - 2,233 Intercompany activity (203,163 ) - - 203,163 - Net cash used in investing activities (336,070 ) (32,434 ) (1,644 ) 203,163 (166,985 ) Financing Activities Borrowings under revolving lines of credit - 2,445,084 19,044 - 2,464,128 Repayments under revolving lines of credit - (2,812,663 ) (20,567 ) - (2,833,230 ) Repayments under term loan (4,500 ) - - - (4,500 ) Repayments under equipment financing facilities and other - (10,049 ) 15 - (10,034 ) Payment of debt issuance costs (1,669 ) - - - (1,669 ) Proceeds from secondary offering of common stock 345,503 - - - 345,503 Payment of issuance costs from secondary offering of common stock (14,684 ) - - - (14,684 ) Proceeds from issuance of common stock related to equity awards 11,341 - - - 11,341 Taxes paid related to net share settlement of equity awards (392 ) - - - (392 ) Excess tax benefit from stock-based compensation 2,937 - - - 2,937 Intercompany activity - 209,018 (2,279 ) (206,739 ) - Net cash provided by (used in) financing activities 338,536 (168,610 ) (3,787 ) (206,739 ) (40,600 ) Effect of exchange rate changes on cash and cash equivalents - - (751 ) - (751 ) Net increase (decrease) in cash and cash equivalents - 112,352 (1,294 ) (4,194 ) 106,864 Cash and cash equivalents, beginning of period - 37,447 2,876 (8,937 ) 31,386 Cash and cash equivalents, end of period $ - $ 149,799 $ 1,582 $ (13,131 ) $ 138,250 BEACON ROOFING SUPPLY, INC. Condensed Consolidating Statements of Cash Flows (Unaudited; In thousands) Year Ended September 30, 2016 Parent Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations and Other Consolidated Net cash provided by (used in) operating activities $ (22,799 ) $ 143,427 $ 4,751 $ (4,731 ) $ 120,648 Investing Activities Purchases of property and equipment (3,654 ) (20,008 ) (2,653 ) - (26,315 ) Acquisition of businesses (1,018,188 ) - - - (1,018,188 ) Proceeds from the sale of assets - 1,882 - - 1,882 Intercompany activity 475,099 - - (475,099 ) - Net cash used in investing activities (546,743 ) (18,126 ) (2,653 ) (475,099 ) (1,042,621 ) Financing Activities Borrowings under revolving lines of credit - 1,877,729 14,730 - 1,892,459 Repayments under revolving lines of credit - (1,520,003 ) (21,529 ) - (1,541,532 ) Borrowings under term loan 490,793 - - - 490,793 Repayments under term loan (230,918 ) - - - (230,918 ) Repayments under equipment financing facilities and other (45 ) (4,659 ) (20 ) - (4,724 ) Borrowings under Senior Notes 300,000 - - - 300,000 Payment of debt issuance costs (19,402 ) (8,923 ) - - (28,325 ) Proceeds from issuance of common stock 24,160 - - - 24,160 Taxes paid related to net share settlement of equity awards (2 ) - - - (2 ) Excess tax benefit from stock-based compensation 4,956 - - - 4,956 Intercompany activity - (474,814 ) (285 ) 475,099 - Net cash provided by (used in) financing activities 569,542 (130,670 ) (7,104 ) 475,099 906,867 Effect of exchange rate changes on cash and cash equivalents - - 831 - 831 Net decrease in cash and cash equivalents - (5,369 ) (4,175 ) (4,731 ) (14,275 ) Cash and cash equivalents, beginning of period - 42,816 7,051 (4,206 ) 45,661 Cash and cash equivalents, end of period $ - $ 37,447 $ 2,876 $ (8,937 ) $ 31,386 BEACON ROOFING SUPPLY, INC. Condensed Consolidating Statements of Cash Flows (Unaudited; In thousands) Year Ended September 30, 2015 Parent Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations and Other Consolidated Net cash provided by operating activities $ 1,776 $ 100,760 $ 4,188 $ 2,616 $ 109,340 Investing Activities Purchases of property and equipment (397 ) (18,649 ) (1,756 ) - (20,802 ) Acquisition of businesses (85,301 ) - - - (85,301 ) Proceeds from the sale of assets - 1,389 - - 1,389 Intercompany activity 93,503 - - (93,503 ) - Net cash provided by (used in) investing activities 7,805 (17,260 ) (1,756 ) (93,503 ) (104,714 ) Financing Activities Borrowings under revolving lines of credit 552,545 - 8,089 - 560,634 Repayments under revolving lines of credit (560,345 ) - (5,662 ) - (566,007 ) Repayments under term loan (11,250 ) - - - (11,250 ) Repayments under equipment financing facilities and other - (5,553 ) - - (5,553 ) Proceeds from issuance of common stock 7,943 - - - 7,943 Excess tax benefit from stock-based compensation 1,526 - - - 1,526 Intercompany activity - (93,184 ) (319 ) 93,503 - Net cash provided by (used in) financing activities (9,581 ) (98,737 ) 2,108 93,503 (12,707 ) Effect of exchange rate changes on cash and cash equivalents - - (730 ) - (730 ) Net increase (decrease) in cash and cash equivalents - (15,237 ) 3,810 2,616 (8,811 ) Cash and cash equivalents, beginning of period - 58,053 3,241 (6,822 ) 54,472 Cash and cash equivalents, end of period $ - $ 42,816 $ 7,051 $ (4,206 ) $ 45,661

Allowance for Doubtful Accounts

Allowance for Doubtful Accounts	12 Months Ended
	Sep. 30, 2017
Allowance For Doubtful Accounts [Abstract]
Allowance for Doubtful Accounts	15. Allowance for Doubtful Accounts The following table summarizes changes in the valuation of the allowance for doubtful accounts (in thousands): Year Ended September 30, Beginning Balance Charged to Operations Write-offs Ending Balance 2017 $ 14,812 $ 2,914 $ (5,897 ) $ 11,829 2016 6,298 13,681 (5,167 ) 14,812 2015 8,510 1,619 (3,831 ) 6,298

Fair Value Measurement

Fair Value Measurement	12 Months Ended
	Sep. 30, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurement	16. Fair Value Measurement As of September 30, 2017, the carrying amount of cash and cash equivalents, accounts receivable, prepaid and other current assets, accounts payable and accrued expenses approximated fair value because of the short-term nature of these instruments. The Company measures its cash equivalents at amortized cost, which approximates fair value based upon quoted market prices (Level 1). Based upon recent trading prices (Level 2 — market approach) as of September 30, 2017 the fair value of the Company’s $300.0 million Senior Notes was $320 million. As of September 30, 2017, the fair value of the Company’s Senior Secured Credit Facility approximated the amount outstanding. The Company estimates the fair value of its Senior Secured Credit Facility by discounting the future cash flows of each instrument using estimated market rates of debt instruments with similar maturities and credit profiles (Level 3).

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Sep. 30, 2017
Compensation And Retirement Disclosure [Abstract]
Benefit Plans	17. Employee Benefit Plans The Company maintains defined contribution plans covering all full-time employees of the Company who have 90 days of service and are at least 21 years old. An eligible employee may elect to make a before-tax contribution of between 1% and 100% of his or her compensation through payroll deductions, not to exceed the annual limit set by law. The Company currently matches the first 50% of participant contributions limited to 6% of a participant’s gross compensation (maximum Company match is 3%). The combined total expense for this plan and a similar plan for Canadian employees was $8.2 million, $7.3 million, and $4.6 million for the years ended September 30, 2017, 2016, and 2015, respectively. The Company also contributes to an external pension fund for certain of its employees who belong to a local union. Annual contributions were $0.1 million for each the years ended September 30, 2017, 2016, and 2015, respectively.

Financial Derivatives

Financial Derivatives	12 Months Ended
	Sep. 30, 2017
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Derivative Instruments and Hedging Activities Disclosure	18. Financial Derivatives The Company has historically used interest rate derivative instruments to manage the risk related to fluctuating cash flows from interest rate changes by converting a portion of its variable-rate borrowings into fixed-rate borrowings. On March 28, 2013, the Company entered into an interest rate swap agreement with a notional amount of $213.8 million which expired on March 31, 2017. This agreement swapped the thirty-day LIBOR to a fixed-rate of 1.38% and had scheduled reductions of the notional amount equal to $2.8 million per quarter, effectively matching the repayment schedule under the Term Loan outstanding at that time. The Company determined this swap agreement qualified for cash flow hedge accounting under ASC 815, therefore changes in the fair value of the swap were recognized through other comprehensive income each period. As of September 30, 2015, the interest rate swap had a notional amount of $185.6 million and a fair value of $2.4 million. On October 1, 2015, in connection with the financing terms surrounding the RSG Acquisition (see Note 3), the Company terminated the swap agreement and settled the $2.4 million unrealized loss with the counterparty. This $2.4 million unrealized loss was recognized on a straight-line basis as interest expense from the termination date through March 31, 2017, the original expiration date of the swap agreement.

Subsequent Events

Subsequent Events	12 Months Ended
	Sep. 30, 2017
Subsequent Events [Abstract]
Subsequent Events	19. Subsequent Events On August 24, 2017, the Company entered into a definitive stock purchase agreement (“the Stock Purchase Agreement”) to acquire, for approximately $2.625 billion in cash (subject to working capital and certain other adjustments as set forth in the Stock Purchase Agreement) (the “Purchase Price”), all of the issued and outstanding shares of capital stock of Allied Building Products Corp. and an affiliated entity (together with its and their respective subsidiaries, “Allied”) on the terms and subject to the conditions set forth in the Stock Purchase Agreement (the “Allied Acquisition”). Allied is one of the country’s largest exterior and interior building products distributors and is headquartered in East Rutherford, New Jersey. The Allied Acquisition is expected to close on January 2, 2018, subject to the satisfaction of customary closing conditions. On October 25, 2017, in connection with the Allied Acquisition, the Company, through a wholly owned finance subsidiary, issued $1.3 billion in aggregate principal amount of 4.875% senior notes due 2025. The funds received in connection with these notes are being held in escrow and will be used to finance the Allied Acquisition, subject to the projected January 2, 2018 closing. In addition, in connection with the Allied Acquisition, the Company secured commitments for the following debt financing facilities: • a $970.0 million seven-year secured term loan “B” facility due 2025 at LIBOR + 2.25% • a $1.3 billion senior-secured asset-based revolving line of credit due 2023 at LIBOR + 1.50% (drawn) and 0.25% (undrawn) Finally, to further finance the Allied Acquisition, on August 24, 2017, in connection with the execution of the Stock Purchase Agreement, the Company entered into an investment agreement (the “Investment Agreement”) with CD&R Boulder Holdings, L.P. (the “CD&R Stockholder”) for the purchase of shares of the Company’s Series A Cumulative Convertible Participating Preferred Stock, par value $0.01 per share (the “Preferred Stock”) in order to partially finance the aggregate Purchase Price. The Preferred Stock will be convertible perpetual participating preferred stock of the Company, with an initial conversion price of $41.26 per share, and accrue dividends at a rate of 6.0% per annum (payable in cash or in-kind, subject to certain conditions). Pursuant to the Investment Agreement, the Company anticipates that it will issue 400,000 shares of Preferred Stock to the CD&R Stockholder with an aggregate liquidation preference of $400 million at a purchase price of $1,000 per share, subject to the projected January 2, 2018 closing.

Summary of Significant Accoun28

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All inter-company transactions have been eliminated. Certain prior period amounts have been reclassified to conform to current period presentation.
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in conformity with United States generally accepted accounting principles (“GAAP”) requires management to make estimates and assumptions that affect the amounts reported in these consolidated financial statements and accompanying notes. Significant items subject to such estimates include inventories, purchase price allocations, recoverability of goodwill and intangibles, and income taxes. Actual amounts could differ from those estimates.
Fiscal Year	Fiscal Year The fiscal years presented are the years ended September 30, 2017 (“2017”), September 30, 2016 (“2016”), and September 30, 2015 (“2015”). Each of the Company’s first three quarters ends on the last day of the calendar month.
Segment Information	Segment Information Operating segments are defined as components of a business that can earn revenue and incur expenses for which discrete financial information is evaluated on a regular basis by the chief operating decision maker (“CODM”) in order to decide how to allocate resources and assess performance. The Company’s CODM, the Chief Executive Officer, reviews consolidated results of operations to make decisions, therefore the Company views its operations and manages its business as one operating segment.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments with maturities of three months or less when purchased to be cash equivalents. Cash and cash equivalents also include unsettled credit card transactions. Cash equivalents are comprised of money market funds which invest primarily in commercial paper or bonds with a rating of A-1 or better, and bank certificates of deposit.
Accounts Receivable	Accounts Receivable Accounts receivables are derived from unpaid invoiced amounts and are recorded at their net realizable value. Each month the Company reviews its receivables on a customer-by-customer basis and evaluates whether an allowance for doubtful accounts is necessary based on any known or perceived collection issues. The allowance for doubtful accounts represents the Company’s estimate of credit exposure for each customer. Any balances that are eventually deemed uncollectible are written off against the allowance after all means of collection have been exhausted and the potential for recovery is considered remote. The Company’s accounts receivable are primarily from customers in the building industry located in the United States and Canada, and no single customer represented at least 10% of the Company’s revenue during the year ended September 30, 2017, or accounts receivable as of September 30, 2017.
Concentrations of Risk	Concentrations of Risk Financial instruments that potentially subject the Company to significant concentration of credit risk consist primarily of cash, cash equivalents and accounts receivable. The Company maintains the majority of its cash and cash equivalents with one financial institution, which management believes to be financially sound and with minimal credit risk. The Company’s deposits periodically exceed amounts guaranteed by the Federal Deposit Insurance Corporation.
Inventories	Inventories Inventories, consisting substantially of finished goods, are valued at the lower of cost or market (net realizable value). Cost is determined using the moving weighted-average cost method. The Company’s arrangements with vendors typically provide for rebates after it makes a special purchase and/or monthly, quarterly and/or annual rebates of a specified amount of consideration payable when a number of measures have been achieved. Annual rebates are generally related to a specified cumulative level of purchases on a calendar-year basis. The Company accounts for such rebates as a reduction of the inventory value until the product is sold, at which time such rebates reduce cost of sales in the consolidated statements of operations. Throughout the year, the Company estimates the amount of the periodic rebates based upon the expected level of purchases. The Company continually revises these estimates to reflect actual rebates earned based on actual purchase levels. Amounts due from vendors under these arrangements are included in “Prepaid expenses and other current assets” in the accompanying consolidated balance sheets.
Property and Equipment	Property and Equipment Property and equipment acquired in connection with acquisitions are recorded at fair value as of the date of the acquisition and depreciated utilizing the straight-line method over the estimated remaining lives. All other additions are recorded at cost, and depreciation is computed using the straight-line method. The Company reviews the estimated useful lives of its fixed assets on an ongoing basis and the following table summarizes the estimates currently used: Asset Class Estimated Useful Life Buildings and improvements 40 years Equipment 3 to 7 years Furniture and fixtures 7 years Leasehold improvements Shorter of the estimated useful life or the term of the lease, considering renewal options expected to be exercised.
Business Combinations	Business Combinations The Company records acquisitions resulting in the consolidation of a business using the acquisition method of accounting. Under this method, the acquiring Company records the assets acquired, including intangible assets that can be identified and named, and liabilities assumed based on their estimated fair values at the date of acquisition. The purchase price in excess of the fair value of the assets acquired and liabilities assumed is recorded as goodwill. Various assumptions are used in the determination of these estimated fair values, including items such sales growth rates, cost synergies, customer attrition rates, discount rates, and other prospective financial information. Estimates associated with the accounting for acquisitions may change as additional information becomes available regarding the assets acquired and liabilities assumed. Transaction costs associated with acquisitions are expensed as incurred.
Goodwill and Intangibles	Goodwill and Intangibles On an annual basis and at interim periods when circumstances require, the Company tests the recoverability of its goodwill and indefinite-lived intangible assets. Examples of such indicators include a significant change in the business climate, unexpected competition, loss of key personnel or a decline in the Company’s market capitalization below the Company’s net book value. The Company performs impairment assessments at the reporting unit level, which is defined as an operating segment or one level below an operating segment, also known as a component. The Company currently has five components which it evaluates for aggregation by examining the distribution methods, sales mix, and operating results of each component to determine if these characteristics will be sustained over a long-term basis. For purposes of this evaluation, the Company expects its components to exhibit similar economic characteristics 3-5 years after events such as an acquisition within the Company’s core roofing business or management/business restructuring. Components that exhibit similar economic characteristics are subsequently aggregated into a single reporting unit. Based on the Company’s most recent impairment assessment performed as of August 31, 2017, it was determined that all of the Company’s components exhibited similar economic characteristics, and therefore should be aggregated into a single reporting unit (collectively the “Reporting Unit”). To test for the recoverability of goodwill and indefinite-lived intangible assets, the Company first performs a qualitative assessment based on economic, industry and company-specific factors for all or selected reporting units to determine whether the existence of events and circumstances indicates that it is more likely than not that the goodwill or indefinite-lived intangible asset is impaired. Based on the results of the qualitative assessment, two additional steps in the impairment assessment may be required. The first step would require a comparison of each reporting unit’s fair value to the respective carrying value. If the carrying value exceeds the fair value, a second step is performed to measure the amount of impairment loss on a relative fair value basis, if any. Based on the Company’s most recent qualitative impairment assessment performed as of August 31, 2017, the Company concluded that there were no indicators of impairment, and that therefore it was more likely than not that the fair value of the goodwill and indefinite-lived intangible assets exceeded their net carrying amount, therefore the quantitative two-step impairment test was not required. The Company amortizes certain identifiable intangible assets that have finite lives, currently consisting of non-compete agreements, customer relationships and trade names. Non-compete agreements are amortized on a straight-line basis over the terms of the associated contractual agreements; customer relationship assets are amortized on an accelerated basis based on the expected cash flows generated by the existing customers; and trade names are amortized on an accelerated basis over a five or ten year period. Amortizable intangible assets are tested for impairment, when deemed necessary, based on undiscounted cash flows and, if impaired, are written down to fair value based on either discounted cash flows or appraised values. In connection with certain financing arrangements, the Company has debt issuance costs that are amortized over the lives of the associated financings using the effective interest method.
Evaluation of Long-Lived Assets	Evaluation of Long-Lived Assets The Company evaluates the recoverability of its long-lived assets for impairment whenever events or circumstances indicate that the carrying amount of the assets may not be recoverable. Recoverability is measured by comparing the carrying amount of the asset to the future undiscounted cash flows the asset is expected to generate. If the asset is considered to be impaired, the amount of any impairment is measured as the difference between the carrying value and the fair value of the impaired asset.
Fair Value Measurement	Fair Value Measurement The Company applies fair value accounting for all financial assets and liabilities that are reported at fair value in the financial statements on a recurring basis. Fair value is defined as the price that would be received from selling an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The accounting guidance establishes a defined three-tier hierarchy to classify and disclose the fair value of assets and liabilities on both the date of their initial measurement as well as all subsequent periods. The hierarchy prioritizes the inputs used to measure fair value by the lowest level of input that is available and significant to the fair value measurement. The three levels are described as follows: • Level 1 : Observable inputs. Quoted prices in active markets for identical assets and liabilities; • Level 2 : Observable inputs other than the quoted price. Includes quoted prices for similar instruments, quoted prices for identical or similar instruments in inactive markets and amounts derived from valuation models where all significant inputs are observable in active markets; and • Level 3 : Unobservable inputs. Includes amounts derived from valuation models where one or more significant inputs are unobservable and require the Company to develop relevant assumptions. The Company evaluates its financial assets and liabilities subject to fair value measurements on a recurring basis to determine the appropriate level of classification as of each reporting period.
Financial Derivatives	Financial Derivatives The Company has entered into interest rate swaps to minimize the risks and costs associated with financing activities, as well as to maintain an appropriate mix of fixed-rate and floating-rate debt. The swap agreements are contracts to exchange variable-rate for fixed-interest rate payments over the life of the agreements. The Company's derivative instruments are designated as cash flow hedges, for which the Company records the effective portions of changes in their fair value, net of tax, in other comprehensive income. The Company recognizes any ineffective portion of the hedges in the consolidated statement of operations through interest expense, financing costs and other.
Net Sales	Net Sales The Company recognizes revenue (net sales on the consolidated statement of operations) when the following four basic criteria are met: • persuasive evidence of an arrangement exists; • delivery has occurred or services have been rendered; • the price to the buyer is fixed and determinable; and • collectability is reasonability assured. Based on these criteria, the Company generally recognizes revenue at the point of sale or upon delivery to the customer site. For goods shipped by third party carriers, the Company recognizes revenue upon shipment since the terms are generally FOB shipping point. The Company also arranges for certain products to be shipped directly from the manufacturer to the customer. The Company recognizes the gross revenue for these sales upon shipment as the terms are FOB shipping point.
Leases	Leases The Company leases the majority of its facilities and enters into various other operating lease agreements in conducting its business. At the inception of each lease, the Company evaluates the lease agreement to determine whether the lease is an operating or capital lease. Operating lease expenses are recognized in the statements of operations on a straight-line basis over the term of the related lease. Some of the Company’s lease agreements may contain renewal options, tenant improvement allowances, rent holidays or rent escalation clauses. When such items are included in a lease agreement, the Company records a deferred rent asset or liability on the consolidated balance sheets equal to the difference between the rent expense and cash rent payments. The cost of property and equipment acquired under capital lease arrangements represents the lesser of the present value of the minimum lease payments or the fair value of the leased asset as of the inception of the lease.
Stock-Based Compensation	Stock-Based Compensation The Company applies the fair value method to recognize compensation expense for stock-based awards. Using this method, the estimated grant-date fair value of the award is recognized on a straight-line basis over the requisite service period based on the portion of the award that is expected to vest. The Company estimates forfeitures at the time of grant and revises the estimates, if necessary, in subsequent periods if actual forfeitures differ from those estimates. For awards with a performance-based vesting condition, the Company accrues stock-based compensation expense if it is probable that the performance condition will be achieved. Stock-based compensation expense for restricted stock units is measured based on the fair value of the Company’s common stock on the grant date. The Company utilizes the Black-Scholes option pricing model to estimate the grant-date fair value of option awards. The exercise price of option awards is set to equal the estimated fair value of the common stock at the date of the grant. The following weighted-average assumptions are also used to calculate the estimated fair value of option awards: • Expected volatility : The expected volatility of the Company’s shares is estimated using the historical stock price volatility over the most recent period commensurate with the estimated expected term of the awards. • Expected term : For employee stock option awards, the Company determines the weighted average expected term equal to the weighted period between the vesting period and the contract life of all outstanding options. • Dividend yield : The Company has not paid dividends and does not anticipate paying a cash dividend in the foreseeable future and, accordingly, uses an expected dividend yield of zero. • Risk-free interest rate : The Company bases the risk-free interest rate on the implied yield available on a U.S. Treasury note with a term equal to the estimated expected term of the awards.
Foreign Currency Translation	Foreign Currency Translation The Company’s operations located outside of the United States where the local currency is the functional currency are translated into U.S. dollars using the current rate method. Results of operations are translated at the average rate of exchange for the period. Assets and liabilities are translated at the closing rates on the period end date. Gains and losses on translation of these accounts are accumulated and reported as a separate component of equity and other comprehensive income (loss). Gains and losses on foreign currency transactions are recognized in the consolidated statements of operations as a component of interest expense, financing costs, and other.
Income Taxes	Income Taxes The Company accounts for income taxes using the liability method, which requires it to recognize a current tax liability or asset for current taxes payable or refundable and a deferred tax liability or asset for the estimated future tax effects of temporary differences between the financial statement and tax reporting bases of assets and liabilities to the extent that they are realizable. Deferred tax expense (benefit) results from the net change in deferred tax assets and liabilities during the year. FASB ASC Topic 740 prescribes a recognition threshold and measurement attribute for the financial statement recognition and measurement of a tax position taken or expected to be taken in a tax return. Based on this guidance, the Company analyzes its filing positions in all of the federal and state jurisdictions where it is required to file income tax returns, as well as all open tax years in these jurisdictions. Tax benefits from uncertain tax positions are recognized if it is more likely than not that the position is sustainable based solely on its technical merits.
Net Income per Share	Net Income per Share The Company’s basic net income per share attributable to common stockholders is calculated by dividing the net income attributable to common stockholders by the weighted-average number of shares of common stock outstanding for the period. The Company’s diluted net income per share is calculated by giving effect to all potentially dilutive common stock equivalents when determining the weighted-average number of common shares outstanding. For purposes of the dilutive net income per share calculation, common shares issuable upon the exercise of stock options or release of restricted stock units are considered to be common stock equivalents.
Recent Accounting Pronouncements - Adopted and Not Yet Adopted	Recent Accounting Pronouncements - Adopted In August 2014, the FASB issued ASU No. 2014-15, “ Presentation of Financial Statements—Going Concern: Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern In April 2015, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2015-03, “ Simplifying the Presentation of Debt Issuance Costs In September 2015, the FASB issued ASU 2015-16, “ Simplifying the Accounting for Measurement-Period Adjustments In November 2015, the FASB issued ASU 2015-17, " Balance Sheet Classification of Deferred Taxes Recent Accounting Pronouncements - Not Yet Adopted In May 2014, the FASB issued ASU 2014-09, “ Revenue from Contracts with Customers In July 2015, the FASB issued ASU 2015-11, “ Inventory: Simplifying the Measurement of Inventory. In February 2016, the FASB issued ASU 2016-02, “ Leases In March 2016, the FASB issued ASU 2016-09, “ Compensation—Stock Compensation: Improvements to Employee Share-Based Payment Accounting.” In June 2016, the FASB issued ASU 2016-13, “ Financial Instruments – Credit Losses: Measurement of Credit Losses on Financial Instruments.” In January 2017, the FASB issued ASU 2017-01, “ Business Combinations: Clarifying the Definition of a Business.” In January 2017, the FASB issued ASU 2017-04, “ Simplifying the Accounting for Goodwill Impairment.” In May 2017, the FASB issued ASU 2017-09, “Scope of Modification Accounting.”

Summary of Significant Accoun29

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Property and Equipment Estimated Useful Life	All other additions are recorded at cost, and depreciation is computed using the straight-line method. The Company reviews the estimated useful lives of its fixed assets on an ongoing basis and the following table summarizes the estimates currently used: Asset Class Estimated Useful Life Buildings and improvements 40 years Equipment 3 to 7 years Furniture and fixtures 7 years Leasehold improvements Shorter of the estimated useful life or the term of the lease, considering renewal options expected to be exercised.

Acquisitions (Tables)

Acquisitions (Tables)	12 Months Ended
	Sep. 30, 2017
Business Combinations [Abstract]
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed	The Company has finalized the acquisition accounting entries for the RSG Acquisition, detailed as follows (in thousands): Cash $ 16,451 Accounts receivable 177,251 Inventory 179,651 Other current assets 50,000 Property, plant, and equipment 55,159 Other intangible assets 382,600 Goodwill 617,477 Current liabilities (252,190 ) Non-current liabilities (56,949 ) Total purchase price $ 1,169,450
Business Acquisition, Pro Forma Information	The following table represents the unaudited pro forma consolidated revenue and net income (loss) for the Company for the prior periods indicated (in thousands, except per share amount): Year Ended September 30, 2015 (unaudited) Net sales $ 3,707,629 Net income 13,051 Net income per share 0.22

Net Income per Share (Tables)

Net Income per Share (Tables)	12 Months Ended
	Sep. 30, 2017
Earnings Per Share [Abstract]
Calculation of Weighted-Average Shares Outstanding	The following table presents the basic and diluted weighted-average shares outstanding for each period presented: Year Ended September 30, 2017 2016 2015 Weighted-average common shares outstanding, basic 60,315,648 59,424,372 49,578,130 Effect of dilutive securities: Stock options 619,732 706,780 481,039 Restricted stock units 408,883 286,915 114,309 Weighted-average common shares outstanding, diluted 61,344,263 60,418,067 50,173,478
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	The following table includes the number of shares that may be dilutive common shares in the future. These shares were not included in the computation of diluted net income per share because the effect was either anti-dilutive or the requisite performance conditions were not met: Year Ended September 30, 2017 2016 2015 Stock options 331,681 502,294 1,313,689 Restricted stock units 61,890 45,220 -

Prepaid Expenses and Other Cu32

Prepaid Expenses and Other Current Assets (Tables)	12 Months Ended
	Sep. 30, 2017
Prepaid Expenses And Other Current Assets [Abstract]
Schedule of Prepaid Expenses and Other Current Assets	The following table summarizes the significant components of prepaid expenses and other current assets (in thousands): September 30, 2017 2016 Vendor rebates $ 193,071 $ 149,052 Other 16,067 14,051 $ 209,138 $ 163,103

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Sep. 30, 2017
Property Plant And Equipment [Abstract]
Property and Equipment, net	The following table provides a detailed breakout of property and equipment, by type (in thousands): September 30, 2017 2016 Land $ 2,796 $ 2,925 Buildings and leasehold improvements 38,995 35,754 Equipment 293,489 263,947 Furniture and fixtures 23,140 20,155 Total property and equipment 358,420 322,781 Less: accumulated depreciation and amortization (202,291 ) (174,212 ) Total property and equipment, net $ 156,129 $ 148,569

Goodwill and Intangibles (Table

Goodwill and Intangibles (Tables)	12 Months Ended
	Sep. 30, 2017
Goodwill And Intangible Assets Disclosure [Abstract]
Summary of Changes in goodwill	The following table sets forth the change in the carrying amount of goodwill for the Company during the years ended September 30, 2017 and 2016 (in thousands): Balance at September 30, 2015 $ 496,415 Acquisition of RSG 617,477 Other acquisitions 84,853 Translation and other adjustments (1,180 ) Balance at September 30, 2016 $ 1,197,565 Acquisitions 53,012 Translation and other adjustments 1,409 Balance at September 30, 2017 $ 1,251,986
Intangibles and Other Assets, Included in Other Long-term Assets	Intangible assets consisted of the following (in thousands, except time period amounts): September 30, Weighted- Average Remaining Life 1 2017 2016 (Years) Amortizable intangible assets: Non-compete agreements $ 2,824 $ 3,324 3.31 Customer relationships 610,026 566,964 17.61 Trademarks 10,500 5,400 8.37 Beneficial lease arrangements 1,060 960 8.79 Total amortizable intangible assets 624,410 576,648 Less: Accumulated amortization (268,391 ) (185,674 ) Total amortizable intangible assets, net $ 356,019 $ 390,974 Indefinite lived trademarks 73,050 73,050 Total intangibles, net $ 429,069 $ 464,024
Estimated Future Annual Amortization	The following table presents the estimated annual amortization expense for these intangible assets (in thousands): Year Ending September 30, 2018 $ 71,577 2019 58,771 2020 47,751 2021 38,248 2022 30,239 Thereafter 109,433 $ 356,019

Financing Arrangements (Tables)

Financing Arrangements (Tables)	12 Months Ended
	Sep. 30, 2017
Debt Disclosure [Abstract]
Schedule of Long-term Debt Instruments	The following table summarizes all financing arrangements the Company has entered into (in thousands): September 30, September 30, 2017 2016 Senior Secured Credit Facility Revolving Lines of Credit: U.S. Revolver, expires October 1, 2020 1 $ - $ 355,087 Canadian Revolver, expires October 1, 2020 2 3,205 4,574 Term Loan, matures October 1, 2022 3 433,440 436,380 Total borrowings under Senior Secured Credit Facility 436,645 796,041 Less: current portion (4,500 ) (4,500 ) Total long-term borrowings under Senior Secured Credit Facility $ 432,145 $ 791,541 Senior Notes Senior Notes, matures October 2023 4 292,328 291,049 Less: current portion - - Total long-term borrowings under Senior Notes $ 292,328 $ 291,049 Equipment Financing Facilities and Other Equipment financing facilities, various maturities through September 2021 5 $ 15,445 $ 20,419 Capital lease obligations, various maturities through November 2021 6 19,956 25,013 Total obligations under equipment financing facilities and other 35,401 45,432 Less: current portion (9,641 ) (10,311 ) Total long-term obligations under equipment financing facilities and other $ 25,760 $ 35,121 1 2 3 4 5 6
Schedule of Maturities of Long-term Debt	Annual principal payments for all outstanding financing arrangements for each of the next five years and thereafter are as follows (in thousands): Year Ending September 30, ABL Term Loan Senior Notes Equipment Financing Facilities Total 2018 $ - $ 4,500 $ - $ 9,584 $ 14,084 2019 - 4,500 - 9,631 14,131 2020 3,205 4,500 - 8,960 16,665 2021 - 4,500 - 4,367 8,867 2022 - 4,500 - 172 4,672 Thereafter - 418,500 300,000 141 718,641 Total debt 3,205 441,000 300,000 32,855 777,060 Less: Unamortized debt issuance costs 1 - (7,560 ) (7,672 ) - (15,232 ) Total long-term debt $ 3,205 $ 433,440 $ 292,328 $ 32,855 $ 761,828 1

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Sep. 30, 2017
Commitments And Contingencies Disclosure [Abstract]
Schedule of Minimum Rental Commitments under Non-cancelable Operating Leases	At September 30, 2017, the minimum rental commitments under all non-cancelable operating leases with initial or remaining terms of more than one year were as follows: Year Ending September 30, Operating Leases 2018 $ 57,075 2019 46,177 2020 37,199 2021 30,350 2022 23,496 Thereafter 29,257 Total minimum lease payments $ 223,554

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Sep. 30, 2017
Equity [Abstract]
Reclassification out of Accumulated Other Comprehensive Income	The following table summarizes the components of accumulated other comprehensive loss (in thousands): Foreign Currency Translation Derivative Financial Instruments Accumulated Other Comprehensive Loss Balance as of September 30, 2014 $ (2,040 ) $ (4,539 ) $ (6,579 ) Other comprehensive loss before reclassifications (14,003 ) (138 ) (14,141 ) Reclassifications out of other comprehensive loss - - - Balance as of September 30, 2015 $ (19,293 ) $ (1,427 ) $ (20,720 ) Other comprehensive income before reclassifications 1,024 - 1,024 Reclassifications out of other comprehensive loss - 1,039 1,039 Balance as of September 30, 2016 $ (18,269 ) $ (388 ) $ (18,657 ) Other comprehensive income before reclassifications 3,706 - 3,706 Reclassifications out of other comprehensive loss - 388 388 Balance as of September 30, 2017 $ (14,563 ) $ - $ (14,563 )

Stock-based Compensation (Table

Stock-based Compensation (Tables)	12 Months Ended
	Sep. 30, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Fair Values of Options, Black-Scholes Option-Pricing Model, Weighted-Average Assumptions	The fair values of the options granted for the year ended September 30, 2017 were estimated on the dates of grants using the Black-Scholes option-pricing model with the following weighted-average assumptions: Year Ended September 30, 2017 2016 2015 Risk-free interest rate 1.97 % 1.87 % 1.83 % Expected volatility 28.83 % 30.96 % 31.69 % Expected life (in years) 5.30 5.6 5.6 Dividend yield — — —
Stock Options Outstanding and Activity During the Period	The following table summarizes all stock option activity for the periods presented (in thousands, except share, per share, and time period amounts): Options Outstanding Weighted- Average Exercise Price Weighted- Average Remaining Contractual Term (Years) Aggregate Intrinsic Value 1 Balance as of September 30, 2016 2,312,789 $ 25.55 6.3 $ 38,225 Granted 245,818 47.40 Exercised (442,909 ) 22.09 Canceled/Forfeited (16,992 ) 33.72 Expired (14,478 ) 19.50 Balance as of September 30, 2017 2,084,228 $ 28.84 6.1 $ 46,714 Vested and expected to vest after September 30, 2017 2,050,134 $ 28.74 6.0 $ 46,150 Exercisable as of September 30, 2017 1,414,141 $ 25.06 5.0 $ 37,033 1 Aggregate intrinsic value as represents the difference between the closing fair value of the underlying common stock and the exercise price of outstanding, in-the-money options on the date of measurement.
Stock Option Grants, Vesting, and Exercises	The following table summarizes additional information on stock options for the period presented (in thousands): Year Ended September 30, 2017 2016 2015 Weighted-average fair value of stock options granted $ 14.21 $ 12.89 $ 9.40 Total fair value of stock options vested 5,566 12,347 6,399 Total intrinsic value of stock options exercised 10,941 22,693 4,615
Restricted Shares and Units Outstanding and Activity During the Period	The following table summarizes all restricted stock unit activity for the periods presented: RSUs Outstanding Weighted-Average Grant Date Fair Value Balance at September 30, 2016 705,434 $ 34.55 Granted 273,065 47.31 Released (128,578 ) 33.47 Canceled/Forfeited (78,948 ) 29.04 Balance at September 30, 2017 770,973 $ 38.95 Vested and expected to vest after September 30, 2017 793,350 $ 38.88
Schedule Of Restricted Stock Units Additional Information	The following table summarizes additional information on RSUs for the period presented (in thousands): Year Ended September 30, 2017 2016 2015 Weighted-average fair value of RSUs granted $ 47.31 $ 38.92 $ 28.74 Total fair value of RSUs vested 4,562 743 1,943 Total intrinsic value of RSUs released 6,079 1,375 1,784

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Schedule Of Income Tax Provision	The following table summarizes the components of the income tax provision (in thousands): Year Ended September 30, 2017 2016 2015 Current: Federal $ 52,718 $ 23,403 $ 17,414 Foreign 1,366 1,183 1,765 State 8,975 2,426 7,579 Total current taxes $ 63,059 $ 27,012 $ 26,758 Deferred: Federal $ (656 ) $ 25,935 $ 14,798 Foreign - 321 (657 ) State 78 3,347 2,868 Total deferred taxes $ (578 ) $ 29,603 $ 17,009 Provision for income taxes $ 62,481 $ 56,615 $ 43,767
Principal Reason for the Difference Between Effective Income Tax Rate and the Statutory Federal Income	The following table is a reconciliation of the statutory federal income tax rate to the Company’s effective income tax rate for the periods presented: Year Ended September 30, 2017 2016 2015 U.S. federal income taxes at statutory rate 35.0 % 35.0 % 35.0 % State income taxes, net of federal benefit 3.9 % 4.2 % 4.6 % Non-deductible professional fees related to RSG acquisition 0.0 % 0.4 % 2.2 % Other (0.6 %) (1.0 %) (0.5 %) Effective tax rate 38.3 % 38.6 % 41.3 %
Components of the Company's Deferred Taxes	temporary differences are determined according to ASC 740 Income Taxes. Temporary differences that give rise to deferred tax assets and liabilities are as follows (in thousands): September 30, 2017 2016 Deferred tax assets: Deferred compensation $ 14,237 $ 15,166 Allowance for doubtful accounts 1,318 2,060 Accrued vacation and other 6,602 6,616 Unrealized loss on financial derivatives - 279 Inventory valuation 10,564 6,193 Tax loss carryforwards 20,575 34,505 Other 958 913 Total deferred tax assets $ 54,254 $ 65,732 Deferred tax liabilities: Excess tax over book depreciation and amortization $ (192,637 ) $ (201,214 ) Total deferred tax liabilities (192,637 ) (201,214 ) Net deferred income tax liabilities $ (138,383 ) $ (135,482 )
Reconciliation of the Beginning and Ending Amounts of Gross Unrecognized Income Tax Benefits	A reconciliation of the beginning and ending amounts of the gross unrecognized income tax benefits is as follows: Year Ended September 30, 2017 2016 Balance, beginning of year $ - $ 82 Current year uncertain tax positions - - Settlements - (82 ) Balance, end of year $ - $ -

Geographic and Product Data (Ta

Geographic and Product Data (Tables)	12 Months Ended
	Sep. 30, 2017
Segment Reporting [Abstract]
Schedule of Geographic Information	The following tables summarize certain geographic information for the periods presented (in thousands): Year Ended September 30, 2017 2016 2015 Net sales U.S. $ 4,198,935 $ 3,949,067 $ 2,331,360 Canada 177,735 178,042 183,809 Total net sales $ 4,376,670 $ 4,127,109 $ 2,515,169 September 30, 2017 2016 Long-lived assets U.S. $ 507,236 $ 527,680 Canada 13,446 13,374 Total long-lived assets $ 520,682 $ 541,054
Schedule Of Net Sales From External Customers By Product Group	The following table summarizes net sales from external customers by product group (in thousands): Year Ended September 30, 2017 2016 2015 Residential roofing products $ 2,380,435 $ 2,190,762 $ 1,236,397 Non-residential roofing products 1,273,153 1,331,319 882,970 Complementary building products 723,082 605,028 395,802 Total net sales $ 4,376,670 $ 4,127,109 $ 2,515,169

Supplemental Guarantor Inform41

Supplemental Guarantor Information (Tables)	12 Months Ended
	Sep. 30, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Condensed Consolidated Balance Sheets	BEACON ROOFING SUPPLY, INC. Condensed Consolidating Balance Sheets (Unaudited; In thousands) September 30, 2017 Parent Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations and Other Consolidated Assets Current assets: Cash and cash equivalents $ - $ 149,799 $ 1,582 $ (13,131 ) $ 138,250 Accounts receivable, net - 663,034 42,633 (1,140 ) 704,527 Inventories, net - 527,226 24,698 - 551,924 Prepaid expenses and other current assets 4,195 198,817 6,126 - 209,138 Total current assets 4,195 1,538,876 75,039 (14,271 ) 1,603,839 Intercompany receivable, net - 655,372 - (655,372 ) - Investments in consolidated subsidiaries 3,160,273 - - (3,160,273 ) - Deferred income taxes, net 30,822 - - (30,822 ) - Property and equipment, net 6,610 138,955 10,564 - 156,129 Goodwill - 1,220,812 31,174 - 1,251,986 Intangibles, net - 426,187 2,882 - 429,069 Other assets, net 2,912 5,622 - - 8,534 Total Assets $ 3,204,812 $ 3,985,824 $ 119,659 $ (3,860,738 ) $ 3,449,557 Liabilities and Stockholders' Equity Current liabilities: Accounts payable $ 27,174 $ 468,891 $ 21,903 $ (14,271 ) $ 503,697 Accrued expenses 51,183 204,173 5,941 - 261,297 Current portions of long-term debt 4,500 9,641 - - 14,141 Total current liabilities 82,857 682,705 27,844 (14,271 ) 779,135 Intercompany payable, net 618,881 - 36,491 (655,372 ) - Borrowings under revolving lines of credit, net - - 3,205 - 3,205 Long-term debt, net 721,268 - - - 721,268 Deferred income taxes, net - 168,209 996 (30,822 ) 138,383 Long-term obligations under equipment financing and other, net - 25,694 66 - 25,760 Total liabilities 1,423,006 876,608 68,602 (700,465 ) 1,667,751 Total stockholders' equity 1,781,806 3,109,216 51,057 (3,160,273 ) 1,781,806 Total Liabilities and Stockholders' Equity $ 3,204,812 $ 3,985,824 $ 119,659 $ (3,860,738 ) $ 3,449,557 BEACON ROOFING SUPPLY, INC. Condensed Consolidating Balance Sheets (Unaudited; In thousands) September 30, 2016 Parent Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations and Other Consolidated Assets Current assets: Cash and cash equivalents $ - $ 37,447 $ 2,876 $ (8,937 ) $ 31,386 Accounts receivable, net - 593,395 34,710 (1,140 ) 626,965 Inventories, net - 460,516 20,220 - 480,736 Prepaid expenses and other current assets 3,527 153,681 5,895 - 163,103 Total current assets 3,527 1,245,039 63,701 (10,077 ) 1,302,190 Intercompany receivable, net - 878,931 - (878,931 ) - Investments in consolidated subsidiaries 2,891,677 - - (2,891,677 ) - Deferred income taxes, net 59,567 - - (59,567 ) - Property and equipment, net 4,626 133,897 10,046 - 148,569 Goodwill - 1,167,905 29,660 - 1,197,565 Intangibles, net - 460,696 3,328 - 464,024 Other assets, net 1,242 269 - - 1,511 Total Assets $ 2,960,639 $ 3,886,737 $ 106,735 $ (3,840,252 ) $ 3,113,859 Liabilities and Stockholders' Equity Current liabilities: Accounts payable $ 26,630 $ 329,895 $ 14,467 $ (10,077 ) $ 360,915 Accrued expenses 42,594 114,016 4,503 - 161,113 Current portions of long-term obligations 4,500 10,311 - - 14,811 Total current liabilities 73,724 454,222 18,970 (10,077 ) 536,839 Intercompany payable, net 840,159 - 38,772 (878,931 ) - Borrowings under revolving lines of credit, net - 355,087 4,574 - 359,661 Long-term debt, net 722,929 - - - 722,929 Deferred income taxes, net - 194,556 493 (59,567 ) 135,482 Long-term obligations under equipment financing and other, net - 35,074 47 - 35,121 Total liabilities 1,636,812 1,038,939 62,856 (948,575 ) 1,790,032 Total stockholders' equity 1,323,827 2,847,798 43,879 (2,891,677 ) 1,323,827 Total Liabilities and Stockholders' Equity $ 2,960,639 $ 3,886,737 $ 106,735 $ (3,840,252 ) $ 3,113,859
Condensed Consolidated Statements of Operations	BEACON ROOFING SUPPLY, INC. Condensed Consolidating Statements of Operations (Unaudited; In thousands, except share and per share amounts) Year Ended September 30, 2017 Parent Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations and Other Consolidated Net sales $ - $ 4,198,935 $ 177,735 $ - $ 4,376,670 Cost of products sold - 3,162,896 137,835 - 3,300,731 Gross profit - 1,036,039 39,900 - 1,075,939 Operating expense 28,496 798,328 33,019 - 859,843 Intercompany charges (income) (4,664 ) 4,342 322 - - Income (loss) from operations (23,832 ) 233,369 6,559 - 216,096 Interest expense, financing costs, and other 38,660 14,033 58 - 52,751 Intercompany interest expense (income) (24,458 ) 22,927 1,531 - - Income (loss) before provision for income taxes (38,034 ) 196,409 4,970 - 163,345 Provision for (benefit from) income taxes (3,284 ) 64,399 1,366 - 62,481 Income (loss) before equity in net income of subsidiaries (34,750 ) 132,010 3,604 - 100,864 Equity in net income of subsidiaries 135,614 - - (135,614 ) - Net income $ 100,864 $ 132,010 $ 3,604 $ (135,614 ) $ 100,864 Weighted-average common stock outstanding: Basic 60,315,648 Diluted 61,344,263 Net income per share: Basic $ 1.67 Diluted $ 1.64 BEACON ROOFING SUPPLY, INC. Condensed Consolidating Statements of Operations (Unaudited; In thousands, except share and per share amounts) Year Ended September 30, 2016 Parent Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations and Other Consolidated Net sales $ - $ 3,949,313 $ 178,042 $ (246 ) $ 4,127,109 Cost of products sold - 2,977,174 137,112 (246 ) 3,114,040 Gross profit - 972,139 40,930 - 1,013,069 Operating expenses 59,949 715,669 32,467 - 808,085 Intercompany charges (income) (51,942 ) 49,285 2,657 - - Income (loss) from operations (8,007 ) 207,185 5,806 - 204,984 Interest expense, financing costs, and other 42,835 14,965 652 - 58,452 Intercompany interest expense (income) (21,536 ) 19,928 1,608 - - Income (loss) before provision for income taxes (29,306 ) 172,292 3,546 - 146,532 Provision for (benefit from) income taxes (472 ) 55,613 1,474 - 56,615 Income (loss) before equity in net income of subsidiaries (28,834 ) 116,679 2,072 - 89,917 Equity in net income of subsidiaries 118,751 - - (118,751 ) - Net income $ 89,917 $ 116,679 $ 2,072 $ (118,751 ) $ 89,917 Weighted-average common stock outstanding: Basic 59,424,372 Diluted 60,418,067 Net income per share: Basic $ 1.51 Diluted $ 1.49 BEACON ROOFING SUPPLY, INC. Condensed Consolidating Statements of Operations (Unaudited; In thousands, except share and per share amounts) Year Ended September 30, 2015 Parent Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations and Other Consolidated Net sales $ - $ 2,331,829 $ 183,809 $ (469 ) $ 2,515,169 Cost of products sold - 1,778,196 142,077 (469 ) 1,919,804 Gross profit - 553,633 41,732 - 595,365 Operating expenses 44,937 399,901 33,446 - 478,284 Intercompany charges (income) (36,085 ) 34,264 1,821 - - Income (loss) from operations (8,852 ) 119,468 6,465 - 117,081 Interest expense, financing costs, and other 9,508 740 789 - 11,037 Intercompany interest expense (income) (15,762 ) 14,174 1,588 - - Income before provision for income taxes (2,598 ) 104,554 4,088 - 106,044 Provision for income taxes (1,087 ) 43,765 1,089 - 43,767 Income before equity in net income of subsidiaries (1,511 ) 60,789 2,999 - 62,277 Equity in net income of subsidiaries 63,788 - - (63,788 ) - Net income $ 62,277 $ 60,789 $ 2,999 $ (63,788 ) $ 62,277 Weighted-average common stock outstanding: Basic 49,578,130 Diluted 50,173,478 Net income per share: Basic $ 1.26 Diluted $ 1.24
Condensed Consolidated Statements of Comprehensive Income	BEACON ROOFING SUPPLY, INC. Condensed Consolidating Statements of Comprehensive Income (Unaudited; In thousands) Year Ended September 30, 2017 Parent Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations and Other Consolidated Net income (loss) $ 100,864 $ 132,010 $ 3,604 $ (135,614 ) $ 100,864 Other comprehensive income: Foreign currency translation adjustment 3,706 - 3,706 (3,706 ) 3,706 Total other comprehensive income 3,706 - 3,706 (3,706 ) 3,706 Comprehensive income (loss) $ 104,570 $ 132,010 $ 7,310 $ (139,320 ) $ 104,570 Year Ended September 30, 2016 Parent Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations and Other Consolidated Net income $ 89,917 $ 116,679 $ 2,072 $ (118,751 ) $ 89,917 Other comprehensive income: Foreign currency translation adjustment 1,024 - 1,024 (1,024 ) 1,024 Total other comprehensive income 1,024 - 1,024 (1,024 ) 1,024 Comprehensive income $ 90,941 $ 116,679 $ 3,096 $ (119,775 ) $ 90,941 Year Ended September 30, 2015 Parent Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations and Other Consolidated Net income $ 62,277 $ 60,789 $ 2,999 $ (63,788 ) $ 62,277 Other comprehensive income (loss): Foreign currency translation adjustment (14,003 ) - (14,003 ) 14,003 (14,003 ) Unrealized loss due to change in fair value of derivatives, net of tax (138 ) - - - (138 ) Total other comprehensive income (loss) (14,141 ) - (14,003 ) 14,003 (14,141 ) Comprehensive income (loss) $ 48,136 $ 60,789 $ (11,004 ) $ (49,785 ) $ 48,136
Condensed Consolidated Statements of Cash Flows	BEACON ROOFING SUPPLY, INC. Condensed Consolidating Statements of Cash Flows (Unaudited; In thousands) Year Ended September 30, 2017 Parent Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations and Other Consolidated Net cash provided by (used in) operating activities $ (2,466 ) $ 313,396 $ 4,888 $ (618 ) $ 315,200 Investing Activities Purchases of property and equipment (3,517 ) (34,584 ) (1,727 ) - (39,828 ) Acquisition of businesses (129,390 ) - - - (129,390 ) Proceeds from the sale of assets - 2,150 83 - 2,233 Intercompany activity (203,163 ) - - 203,163 - Net cash used in investing activities (336,070 ) (32,434 ) (1,644 ) 203,163 (166,985 ) Financing Activities Borrowings under revolving lines of credit - 2,445,084 19,044 - 2,464,128 Repayments under revolving lines of credit - (2,812,663 ) (20,567 ) - (2,833,230 ) Repayments under term loan (4,500 ) - - - (4,500 ) Repayments under equipment financing facilities and other - (10,049 ) 15 - (10,034 ) Payment of debt issuance costs (1,669 ) - - - (1,669 ) Proceeds from secondary offering of common stock 345,503 - - - 345,503 Payment of issuance costs from secondary offering of common stock (14,684 ) - - - (14,684 ) Proceeds from issuance of common stock related to equity awards 11,341 - - - 11,341 Taxes paid related to net share settlement of equity awards (392 ) - - - (392 ) Excess tax benefit from stock-based compensation 2,937 - - - 2,937 Intercompany activity - 209,018 (2,279 ) (206,739 ) - Net cash provided by (used in) financing activities 338,536 (168,610 ) (3,787 ) (206,739 ) (40,600 ) Effect of exchange rate changes on cash and cash equivalents - - (751 ) - (751 ) Net increase (decrease) in cash and cash equivalents - 112,352 (1,294 ) (4,194 ) 106,864 Cash and cash equivalents, beginning of period - 37,447 2,876 (8,937 ) 31,386 Cash and cash equivalents, end of period $ - $ 149,799 $ 1,582 $ (13,131 ) $ 138,250 BEACON ROOFING SUPPLY, INC. Condensed Consolidating Statements of Cash Flows (Unaudited; In thousands) Year Ended September 30, 2016 Parent Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations and Other Consolidated Net cash provided by (used in) operating activities $ (22,799 ) $ 143,427 $ 4,751 $ (4,731 ) $ 120,648 Investing Activities Purchases of property and equipment (3,654 ) (20,008 ) (2,653 ) - (26,315 ) Acquisition of businesses (1,018,188 ) - - - (1,018,188 ) Proceeds from the sale of assets - 1,882 - - 1,882 Intercompany activity 475,099 - - (475,099 ) - Net cash used in investing activities (546,743 ) (18,126 ) (2,653 ) (475,099 ) (1,042,621 ) Financing Activities Borrowings under revolving lines of credit - 1,877,729 14,730 - 1,892,459 Repayments under revolving lines of credit - (1,520,003 ) (21,529 ) - (1,541,532 ) Borrowings under term loan 490,793 - - - 490,793 Repayments under term loan (230,918 ) - - - (230,918 ) Repayments under equipment financing facilities and other (45 ) (4,659 ) (20 ) - (4,724 ) Borrowings under Senior Notes 300,000 - - - 300,000 Payment of debt issuance costs (19,402 ) (8,923 ) - - (28,325 ) Proceeds from issuance of common stock 24,160 - - - 24,160 Taxes paid related to net share settlement of equity awards (2 ) - - - (2 ) Excess tax benefit from stock-based compensation 4,956 - - - 4,956 Intercompany activity - (474,814 ) (285 ) 475,099 - Net cash provided by (used in) financing activities 569,542 (130,670 ) (7,104 ) 475,099 906,867 Effect of exchange rate changes on cash and cash equivalents - - 831 - 831 Net decrease in cash and cash equivalents - (5,369 ) (4,175 ) (4,731 ) (14,275 ) Cash and cash equivalents, beginning of period - 42,816 7,051 (4,206 ) 45,661 Cash and cash equivalents, end of period $ - $ 37,447 $ 2,876 $ (8,937 ) $ 31,386 BEACON ROOFING SUPPLY, INC. Condensed Consolidating Statements of Cash Flows (Unaudited; In thousands) Year Ended September 30, 2015 Parent Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations and Other Consolidated Net cash provided by operating activities $ 1,776 $ 100,760 $ 4,188 $ 2,616 $ 109,340 Investing Activities Purchases of property and equipment (397 ) (18,649 ) (1,756 ) - (20,802 ) Acquisition of businesses (85,301 ) - - - (85,301 ) Proceeds from the sale of assets - 1,389 - - 1,389 Intercompany activity 93,503 - - (93,503 ) - Net cash provided by (used in) investing activities 7,805 (17,260 ) (1,756 ) (93,503 ) (104,714 ) Financing Activities Borrowings under revolving lines of credit 552,545 - 8,089 - 560,634 Repayments under revolving lines of credit (560,345 ) - (5,662 ) - (566,007 ) Repayments under term loan (11,250 ) - - - (11,250 ) Repayments under equipment financing facilities and other - (5,553 ) - - (5,553 ) Proceeds from issuance of common stock 7,943 - - - 7,943 Excess tax benefit from stock-based compensation 1,526 - - - 1,526 Intercompany activity - (93,184 ) (319 ) 93,503 - Net cash provided by (used in) financing activities (9,581 ) (98,737 ) 2,108 93,503 (12,707 ) Effect of exchange rate changes on cash and cash equivalents - - (730 ) - (730 ) Net increase (decrease) in cash and cash equivalents - (15,237 ) 3,810 2,616 (8,811 ) Cash and cash equivalents, beginning of period - 58,053 3,241 (6,822 ) 54,472 Cash and cash equivalents, end of period $ - $ 42,816 $ 7,051 $ (4,206 ) $ 45,661

Allowance for Doubtful Accoun42

Allowance for Doubtful Accounts (Tables)	12 Months Ended
	Sep. 30, 2017
Allowance For Doubtful Accounts [Abstract]
Allowance for Doubtful Accounts	The following table summarizes changes in the valuation of the allowance for doubtful accounts (in thousands): Year Ended September 30, Beginning Balance Charged to Operations Write-offs Ending Balance 2017 $ 14,812 $ 2,914 $ (5,897 ) $ 11,829 2016 6,298 13,681 (5,167 ) 14,812 2015 8,510 1,619 (3,831 ) 6,298

Company Overview - Additional I

Company Overview - Additional Information (Detail)	12 Months Ended
	Sep. 30, 2017StateProvince
Company Overview [Line Items]
Date of incorporation	Aug. 22, 1997
United States
Company Overview [Line Items]
Number of states in which entity operates | State	48
Canada
Company Overview [Line Items]
Number of provinces in which entity operates | Province	6

Summary of Significant Accoun44

Summary of Significant Accounting Policies - Additional Information (Detail) $ in Thousands	12 Months Ended
	Sep. 30, 2017USD ($)SegmentCustomer	Sep. 30, 2016USD ($)	Sep. 30, 2015USD ($)
Significant Accounting Policies [Line Items]
Number of operating segments | Segment	1
Number of customers, with at least 10% of revenue | Customer	0
Number of customers, with at least 10% of accounts receivable | Customer	0
Expected dividend yield	0.00%	0.00%	0.00%
Debt related commitment fees and debt issuance costs | $	$ 20,600	$ 25,200
Deferred Tax Assets, Net, Noncurrent | $	$ 0	$ 0	$ 2,300
Trade Names [Member]
Significant Accounting Policies [Line Items]
Finite-lived intangible assets, amortization method	accelerated basis over a five or ten year period
Minimum [Member]
Significant Accounting Policies [Line Items]
Amortization period	5 years
Minimum [Member] | Trade Names [Member]
Significant Accounting Policies [Line Items]
Amortization period	5 years
Maximum [Member]
Significant Accounting Policies [Line Items]
Amortization period	20 years
Maximum [Member] | Trade Names [Member]
Significant Accounting Policies [Line Items]
Amortization period	10 years
Major Supplier Concentration Risk [Member] | Minimum [Member] | Cost of Goods, Total [Member]
Significant Accounting Policies [Line Items]
Goodwill impairment test period	3 years
Major Supplier Concentration Risk [Member] | Maximum [Member] | Cost of Goods, Total [Member]
Significant Accounting Policies [Line Items]
Goodwill impairment test period	5 years

Summary of Significant Accoun45

Summary of Significant Accounting Policies - Summary of Property and Equipment Estimated Useful Life (Detail)	12 Months Ended
	Sep. 30, 2017
Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	40 years
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	7 years
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	Shorter of the estimated useful life or the term of the lease, considering renewal options expected to be exercised.
Minimum [Member] | Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	3 years
Maximum [Member] | Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	7 years

Acquisitions - Additional Infor

Acquisitions - Additional Information (Detail) $ in Thousands

May 01, 2017USD ($)Location

Mar. 01, 2017USD ($)Location

Jan. 09, 2017USD ($)Location

Jan. 03, 2017USD ($)Location

Dec. 16, 2016USD ($)Location

Jun. 01, 2016USD ($)Location

May 02, 2016USD ($)Location

Apr. 01, 2016USD ($)Location

Dec. 29, 2015USD ($)Location

Dec. 18, 2015USD ($)StateLocation

Dec. 01, 2015USD ($)Location

Oct. 02, 2015USD ($)shares

Sep. 30, 2017USD ($)BranchBusiness

Sep. 30, 2016USD ($)BranchBusiness

Sep. 30, 2015USD ($)

Oct. 01, 2015USD ($)Location

Business Acquisition [Line Items]

Number Of Business Locations Acquired | Branch

23

42

Business Acquisition, Goodwill, Expected Tax Deductible Amount

$ 59,800

$ 86,100

Business Combination, Acquired Receivables, Fair Value

177,300

Business Combination, Acquired Receivables, Gross Contractual Amount

$ 185,900

Revenue, Net

$ 4,376,670

$ 4,127,109

$ 2,515,169

Number Of Business Locations Acquired | Business

5

7

Business Acquisition, sales reported by acquired entity for last annual period

3,707,629

Business Acquisitions Purchase Price Allocation Goodwill Amount

$ 1,251,986

$ 1,197,565

496,415

Roofing Supply Groups

Business Acquisition [Line Items]

Business Acquisition, Percentage of Voting Interests Acquired

100.00%

Number Of Business Locations Acquired | Location

85

Number Of States Business Location Acquired | Location

25

Business Combination, Consideration Transferred, Total

$ 1,170,000

Payments to Acquire Businesses, Gross

288,200

Business Combination, Consideration Transferred, Other

306,800

Business Combination, Consideration Transferred, Liabilities Incurred

$ 574,400

Options to purchase common stock | shares

661,349

Revenue, Net

1,400,000

Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual

10,300

Business Acquisition, Transaction Costs

$ 58,200

Business Acquisitions Purchase Price Allocation Goodwill Amount

617,477

Business Acquisitions Purchase Price Allocation Intangible Assets Other Than Goodwill

382,600

BJ Supply Company

Business Acquisition [Line Items]

Number Of Business Locations Acquired | Location

1

Business Acquisition, sales reported by acquired entity for last annual period

$ 4,000

American Building and Roofing, Inc

Business Acquisition [Line Items]

Number Of Business Locations Acquired | Location

7

Business Acquisition, sales reported by acquired entity for last annual period

$ 36,000

Eco Insulation Supply [Member]

Business Acquisition [Line Items]

Number Of Business Locations Acquired | Location

1

Business Acquisition, sales reported by acquired entity for last annual period

$ 8,000

Acme Building Materials Inc

Business Acquisition [Line Items]

Number Of Business Locations Acquired | Location

3

Business Acquisition, sales reported by acquired entity for last annual period

$ 13,000

Lowry's Inc.

Business Acquisition [Line Items]

Number Of Business Locations Acquired | Location

11

Business Acquisition, sales reported by acquired entity for last annual period

$ 76,000

Series of Individually Immaterial Business Acquisitions

Business Acquisition [Line Items]

Business Acquisitions Purchase Price Allocation Goodwill Amount

53,000

84,800

Business Acquisitions Purchase Price Allocation Intangible Assets Other Than Goodwill

$ 47,400

$ 60,800

RCI Roofing Supply [Member]

Business Acquisition [Line Items]

Number Of Business Locations Acquired | Location

5

Business Acquisition, sales reported by acquired entity for last annual period

$ 23,000

Roofing and Insulation Supply

Business Acquisition [Line Items]

Business Acquisition, Percentage of Voting Interests Acquired

100.00%

Number Of Business Locations Acquired | Location

20

Number Of States Business Location Acquired | State

13

Business Acquisition, sales reported by acquired entity for last annual period

$ 70,000

Statewide Wholesale

Business Acquisition [Line Items]

Number Of Business Locations Acquired | Location

1

Business Acquisition, sales reported by acquired entity for last annual period

$ 15,000

Atlantic Building Product [Member]

Business Acquisition [Line Items]

Number Of Business Locations Acquired | Location

2

Business Acquisition, sales reported by acquired entity for last annual period

$ 5,000

Lyf-Tym Building Product

Business Acquisition [Line Items]

Number Of Business Locations Acquired | Location

6

Business Acquisition, sales reported by acquired entity for last annual period

$ 20,000

Fox Brothers [Member]

Business Acquisition [Line Items]

Number Of Business Locations Acquired | Location

4

Business Acquisition, sales reported by acquired entity for last annual period

$ 35,000

Woodfeathers Inc [Member]

Business Acquisition [Line Items]

Business Acquisition, Percentage of Voting Interests Acquired

100.00%

Number Of Business Locations Acquired | Location

4

Business Acquisition, sales reported by acquired entity for last annual period

$ 30,000

Acquisitions - Schedule of Reco

Acquisitions - Schedule of Recognized Identified Assets Acquired and Liabilities Assumed (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Business Combination, Separately Recognized Transactions [Line Items]
Goodwill	$ 1,251,986	$ 1,197,565	$ 496,415
Roofing Supply Groups
Business Combination, Separately Recognized Transactions [Line Items]
Cash	16,451
Accounts receivable	177,251
Inventory	179,651
Other current assets	50,000
Property, plant, and equipment	55,159
Other intangible assets	382,600
Goodwill	617,477
Current liabilities	(252,190)
Non-current liabilities	(56,949)
Total purchase price	$ 1,169,450

Acquisitions - Business Acquisi

Acquisitions - Business Acquisition, Pro Forma Information (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Sep. 30, 2015USD ($)$ / shares
Business Combinations [Abstract]
Net sales	$ 3,707,629
Net income	$ 13,051
Net income per share | $ / shares	$ 0.22

Net Income per Share - Calculat

Net Income per Share - Calculation of Weighted-Average Shares Outstanding (Detail) - shares	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Weighted Average Number of Shares Outstanding [Line Items]
Weighted-average common shares outstanding, basic	60,315,648	59,424,372	49,578,130
Effect of dilutive securities:
Weighted-average common shares outstanding, diluted	61,344,263	60,418,067	50,173,478
Stock Options [Member]
Effect of dilutive securities:
Weighted Average Number Diluted Shares Outstanding Adjustment	619,732	706,780	481,039
Restricted Stock [Member]
Effect of dilutive securities:
Weighted Average Number Diluted Shares Outstanding Adjustment	408,883	286,915	114,309

Net Income per Share - Schedule

Net Income per Share - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Detail) - shares	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	331,681	502,294	1,313,689
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	61,890	45,220	0

Prepaid Expenses and Other Cu51

Prepaid Expenses and Other Current Assets - Schedule of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Sep. 30, 2016
Prepaid Expenses And Other Current Assets [Abstract]
Vendor rebates	$ 193,071	$ 149,052
Other	16,067	14,051
Prepaid Expense and Other Assets, Current	$ 209,138	$ 163,103

Property and Equipment - Proper

Property and Equipment - Property and Equipment, net (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Sep. 30, 2016
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 358,420	$ 322,781
Less: accumulated depreciation and amortization	(202,291)	(174,212)
Total property and equipment, net	156,129	148,569
Land [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	2,796	2,925
Buildings And Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	38,995	35,754
Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	293,489	263,947
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 23,140	$ 20,155

Property and Equipment - Additi

Property and Equipment - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2014
Property Plant And Equipment [Abstract]
Depreciation	$ 34	$ 31.9	$ 18.7

Goodwill and Intangibles - Summ

Goodwill and Intangibles - Summary of Changes in goodwill (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Goodwill [Line Items]
Beginning balance	$ 1,197,565	$ 496,415
Acquisition	53,012
Translation and other adjustments	1,409	(1,180)
Ending balance	1,251,986	1,197,565
Roofing Supply Groups
Goodwill [Line Items]
Acquisition		617,477
Ending balance	$ 617,477
All Other Acquisitions [Member]
Goodwill [Line Items]
Acquisition		$ 84,853

Goodwill and Intangible - Addit

Goodwill and Intangible - Additional Information (Details) (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Goodwill And Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired	$ 47.4
Amortization of Intangible Assets	$ 82.5	$ 68.3	$ 16.2
Minimum [Member]
Goodwill And Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	5 years
Maximum [Member]
Goodwill And Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	20 years
Weighted Average [Member]
Goodwill And Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	17 years 4 months 25 days
Customer Relationships [Member]
Goodwill And Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired	$ 42.7
Customer Relationships [Member] | Weighted Average [Member]
Goodwill And Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	17 years 7 months 10 days
Trademarks [Member]
Goodwill And Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired	$ 4.6
Trademarks [Member] | Weighted Average [Member]
Goodwill And Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	8 years 4 months 13 days
Beneficial Lease Arrangements [Member]
Goodwill And Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired	$ 0.1
Beneficial Lease Arrangements [Member] | Weighted Average [Member]
Goodwill And Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	8 years 9 months 14 days

Goodwill and Intangible - Intan

Goodwill and Intangible - Intangibles and Other Assets, Included in Other Long-term Assets (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Finite Lived Intangible Assets [Line Items]
Amortizable intangible assets:	$ 624,410	$ 576,648
Less: Accumulated amortization	(268,391)	(185,674)
Total amortizable intangible assets, net	356,019	390,974
Indefinite lived trademarks	73,050	73,050
Total intangibles, net	$ 429,069	464,024
Weighted Average [Member]
Finite Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	17 years 4 months 25 days
Minimum [Member]
Finite Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	5 years
Maximum [Member]
Finite Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	20 years
Noncompete Agreements [Member]
Finite Lived Intangible Assets [Line Items]
Amortizable intangible assets:	$ 2,824	3,324
Noncompete Agreements [Member] | Weighted Average [Member]
Finite Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	3 years 3 months 22 days
Customer Relationships [Member]
Finite Lived Intangible Assets [Line Items]
Amortizable intangible assets:	$ 610,026	566,964
Customer Relationships [Member] | Weighted Average [Member]
Finite Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	17 years 7 months 10 days
Trademarks [Member]
Finite Lived Intangible Assets [Line Items]
Amortizable intangible assets:	$ 10,500	5,400
Trademarks [Member] | Weighted Average [Member]
Finite Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	8 years 4 months 13 days
Beneficial Lease Arrangements [Member]
Finite Lived Intangible Assets [Line Items]
Amortizable intangible assets:	$ 1,060	$ 960
Beneficial Lease Arrangements [Member] | Weighted Average [Member]
Finite Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	8 years 9 months 14 days

Goodwill and Intangible - Estim

Goodwill and Intangible - Estimated Future Annual Amortization (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Sep. 30, 2016
Goodwill And Intangible Assets Disclosure [Abstract]
2,018	$ 71,577
2,019	58,771
2,020	47,751
2,021	38,248
2,022	30,239
Thereafter	109,433
Total amortizable intangible assets, net	$ 356,019	$ 390,974

Financing Arrangements - Additi

Financing Arrangements - Additional Information (Detail)		Sep. 30, 2017USD ($)Covenant	Sep. 16, 2016USD ($)	Oct. 02, 2015USD ($)	Dec. 31, 2015USD ($)	Sep. 30, 2017USD ($)Covenant	Sep. 30, 2016USD ($)	Sep. 30, 2015USD ($)
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity				$ 1,450,000,000
Borrowings under Senior Notes						$ 0	$ 300,000,000	$ 0
Unamortized debt issuance costs	[1]	$ 15,232,000				$ 15,232,000
Maximum percentage of borrowing availability to in effect covenant applicability						10.00%
Amortization of Debt Issuance Costs			$ 1,600,000
LIBOR floor rate			0.25%
LIBOR spread rate			0.25%
Debt related commitment fees and debt issuance costs						$ 20,600,000	25,200,000
Term Loan [Member]
Debt Instrument [Line Items]
Long-term Line of Credit		433,400,000		$ 450,000,000		433,400,000
Debt Instrument, Maturity Date				Oct. 1, 2022
Unamortized debt issuance costs	[1]	7,560,000				$ 7,560,000
Debt Instrument, Periodic Payment				$ 1,100,000
Debt Instrument, Frequency of Periodic Payment						quarterly
Debt Instrument, Description Of Change In Interest Rate						lowering the LIBOR floor by 25 basis points and lowering the spread by 25 basis points
Senior Notes [Member]
Debt Instrument [Line Items]
Borrowings under Senior Notes				$ 300,000,000
Debt Instrument, Maturity Date				Oct. 1, 2023		Oct. 1, 2023
Unamortized debt issuance costs	[1]	7,672,000				$ 7,672,000
Debt instrument, coupon rate				6.38%
Senior Notes, matures October 2023	[2]	292,328,000				$ 292,328,000	291,049,000
Unsecured Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument maturity year						2,020
Equipment Financing Facilities [Member]
Debt Instrument [Line Items]
Equipment financing facilities, various maturities through September 2021		$ 15,400,000				$ 15,400,000
Equipment Financing Facilities and Other [Member] | Minimum [Member]
Debt Instrument [Line Items]
Percentage of Fixed Interest Rate of Equipment Financing Facilities		2.33%
Equipment Financing Facilities and Other [Member] | Maximum [Member]
Debt Instrument [Line Items]
Percentage of Fixed Interest Rate of Equipment Financing Facilities		3.25%
Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date						Nov. 30, 2021
Capital lease obligations, various maturities through November 2021	[3]	$ 19,956,000				$ 19,956,000	$ 25,013,000
Capital Lease Obligations [Member] | Minimum [Member]
Debt Instrument [Line Items]
Capital Leases of Lessor, Contingent Rentals, Basis Spread on Variable Rate		2.72%				2.72%	2.72%
Capital Lease Obligations [Member] | Maximum [Member]
Debt Instrument [Line Items]
Capital Leases of Lessor, Contingent Rentals, Basis Spread on Variable Rate		10.39%				10.39%	10.39%
Roofing Supply Group [Member]
Debt Instrument [Line Items]
Payments of Financing Costs, Total							$ 31,300,000
ABL Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity				$ 700,000,000
Proceeds from Lines of Credit				$ 350,000,000
Long-term Line of Credit		$ 3,200,000				$ 3,200,000
Debt Instrument, Maturity Date				Oct. 1, 2020
Debt Instrument, Weighted average interest rate		2.00%				2.00%
Unamortized debt issuance costs	[1]	$ 0				$ 0
Line of credit facility, unused fees						0.25%
Number of financial covenants | Covenant		1				1
Fixed charge coverage ratio		100.00%				100.00%
Debt Instrument, Covenant Description						The covenant is only applicable when the borrowing availability is less than 10% of the maximum loan cap or $60.0 million.
Maximum borrowing availability for covenant applicability		$ 60,000,000				$ 60,000,000
ABL Facility [Member] | Other Assets, Net [Member]
Debt Instrument [Line Items]
Unamortized debt issuance costs		5,300,000				$ 5,300,000
ABL Facility [Member] | Base Rate [Member]
Debt Instrument [Line Items]
Debt Instrument, interest rate spread						4.75%
ABL Facility [Member] | Tranche One [Member]
Debt Instrument [Line Items]
Debt Instrument, interest rate spread						1.25%
ABL Facility [Member] | Tranche Two [Member]
Debt Instrument [Line Items]
Debt Instrument, interest rate spread						1.50%
ABL Facility [Member] | Tranche Three [Member]
Debt Instrument [Line Items]
Debt Instrument, interest rate spread						1.75%
ABL Facility [Member] | U.S. [Member]
Debt Instrument [Line Items]
Long-term Line of Credit				$ 670,000,000
Standby letters of credit outstanding		$ 10,800,000				$ 10,800,000
ABL Facility [Member] | Canada [Member]
Debt Instrument [Line Items]
Long-term Line of Credit				$ 30,000,000
New Senior Credit Facilities [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Debt related commitment fees and debt issuance costs							$ 2,200,000
Gains (Losses) on Extinguishment of Debt					$ 800,000
[1]	Does not include $5.3 million of unamortized debt issuance costs related to the ABL classified as “other assets, net” on the consolidated balance sheet as of September 30, 2017
[2]	Interest rate of 6.38% as of September 30, 2017 and September 30, 2016
[3]	Fixed interest rates ranging from 2.72% to 10.39% as of September 30, 2017 and September 30, 2016

Financing Arrangements - Long-t

Financing Arrangements - Long-term Debt Instruments (Detail) - USD ($) $ in Thousands		Sep. 30, 2017	Sep. 30, 2016
Debt Instrument [Line Items]
Total long-term borrowings under Senior Secured Credit Facility		$ 3,205	$ 359,661
Total long-term obligations under equipment financing facilities and other		25,760	35,121
Senior Notes [Member]
Debt Instrument [Line Items]
Senior Notes, matures October 2023	[1]	292,328	291,049
Less: current portion		0	0
Total long-term borrowings under Senior Notes		292,328	291,049
Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Capital lease obligations, various maturities through November 2021	[2]	19,956	25,013
Equipment Financing Facilities [Member]
Debt Instrument [Line Items]
Equipment financing facilities, various maturities through September 2021	[3]	15,445	20,419
Senior Secured Credit Facility
Debt Instrument [Line Items]
Total borrowings under Senior Secured Credit Facility		436,645	796,041
Less: current portion		(4,500)	(4,500)
Total long-term borrowings under Senior Secured Credit Facility		432,145	791,541
Senior Secured Credit Facility | Term Loan [Member]
Debt Instrument [Line Items]
Total borrowings under Senior Secured Credit Facility		433,440	436,380
Senior Secured Credit Facility | U.S. [Member]
Debt Instrument [Line Items]
Total borrowings under Senior Secured Credit Facility	[4]		355,087
Senior Secured Credit Facility | Canada [Member]
Debt Instrument [Line Items]
Total borrowings under Senior Secured Credit Facility	[5]	3,205	4,574
Equipment Financing Facilities and Other [Member]
Debt Instrument [Line Items]
Total obligations under equipment financing facilities and other		35,401	45,432
Less: current portion		(9,641)	(10,311)
Total long-term obligations under equipment financing facilities and other		$ 25,760	$ 35,121
[1]	Interest rate of 6.38% as of September 30, 2017 and September 30, 2016
[2]	Fixed interest rates ranging from 2.72% to 10.39% as of September 30, 2017 and September 30, 2016
[3]	Fixed interest rates ranging from 2.33% to 3.25% as of September 30, 2017 and September 30, 2016
[4]	Effective rates on borrowings are 2.00% as of September 30, 2017; 2.90% as of September 30, 2016
[5]	Effective rates on borrowings are 3.70% as of September 30, 2017; 3.20% as of September 30, 2016

Financing Arrangements - Long60

Financing Arrangements - Long-term Debt Instruments (Parenthetical) (Detail)	Oct. 02, 2015	Sep. 30, 2017	Sep. 30, 2016
Equipment Financing Facilities [Member]
Debt Instrument [Line Items]
Debt instrument maturity date		Sep. 30, 2021
Equipment Financing Facilities [Member] | Minimum [Member]
Debt Instrument [Line Items]
Equipment financing facilities, fixed interest rate percentage		2.33%	2.33%
Equipment Financing Facilities [Member] | Maximum [Member]
Debt Instrument [Line Items]
Equipment financing facilities, fixed interest rate percentage		3.25%	3.25%
Senior Secured Credit Facility | Term Loan [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Interest Rate at Period End		3.50%	3.50%
Line of Credit Facility, Expiration Date		Oct. 1, 2022
Senior Secured Credit Facility | U.S. [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Interest Rate at Period End		2.00%	2.90%
Line of Credit Facility, Expiration Date		Oct. 1, 2020
Senior Secured Credit Facility | Canada [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Interest Rate at Period End		3.70%	3.20%
Line of Credit Facility, Expiration Date		Oct. 1, 2020
Senior Notes [Member]
Debt Instrument [Line Items]
Senior Notes, Interest Rate at Period End		6.38%	6.38%
Debt instrument maturity date	Oct. 1, 2023	Oct. 1, 2023
Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Debt instrument maturity date		Nov. 30, 2021
Capital Lease Obligations [Member] | Minimum [Member]
Debt Instrument [Line Items]
Capital lease obligations, fixed interest rate percentage		2.72%	2.72%
Capital Lease Obligations [Member] | Maximum [Member]
Debt Instrument [Line Items]
Capital lease obligations, fixed interest rate percentage		10.39%	10.39%

Financing Arrangements - Schedu

Financing Arrangements - Schedule of Maturities of Long-term Debt (Detail) $ in Thousands	Sep. 30, 2017USD ($)
Debt Instrument [Line Items]
2,018	$ 14,084
2,019	14,131
2,020	16,665
2,021	8,867
2,022	4,672
Thereafter	718,641
Total debt	777,060
Less: Unamortized debt issuance costs	(15,232)	[1]
Total long-term debt	761,828
ABL Facility [Member]
Debt Instrument [Line Items]
2,018	0
2,019	0
2,020	3,205
2,021	0
2,022	0
Thereafter	0
Total debt	3,205
Less: Unamortized debt issuance costs	0	[1]
Total long-term debt	3,205
Equipment Financing Facilities [Member]
Debt Instrument [Line Items]
2,018	9,584
2,019	9,631
2,020	8,960
2,021	4,367
2,022	172
Thereafter	141
Total debt	32,855
Less: Unamortized debt issuance costs	0	[1]
Total long-term debt	32,855
Term Loan [Member]
Debt Instrument [Line Items]
2,018	4,500
2,019	4,500
2,020	4,500
2,021	4,500
2,022	4,500
Thereafter	418,500
Total debt	441,000
Less: Unamortized debt issuance costs	(7,560)	[1]
Total long-term debt	433,440
Senior Notes [Member]
Debt Instrument [Line Items]
2,018	0
2,019	0
2,020	0
2,021	0
2,022	0
Thereafter	300,000
Total debt	300,000
Less: Unamortized debt issuance costs	(7,672)	[1]
Total long-term debt	$ 292,328
[1]	Does not include $5.3 million of unamortized debt issuance costs related to the ABL classified as “other assets, net” on the consolidated balance sheet as of September 30, 2017

Financing Arrangements - Sche62

Financing Arrangements - Schedule of Maturities of Long-term Debt (Detail) (Parenthetical) (Detail) $ in Thousands	Sep. 30, 2017USD ($)
Debt Instrument [Line Items]
Unamortized debt issuance costs	$ 15,232	[1]
ABL Facility [Member]
Debt Instrument [Line Items]
Unamortized debt issuance costs	0	[1]
ABL Facility [Member] | Other Assets, Net [Member]
Debt Instrument [Line Items]
Unamortized debt issuance costs	$ 5,300
[1]	Does not include $5.3 million of unamortized debt issuance costs related to the ABL classified as “other assets, net” on the consolidated balance sheet as of September 30, 2017

Commitments and Contingencies -

Commitments and Contingencies - Schedule of Minimum Rental Commitments under Non-cancelable Operating Leases (Detail) $ in Thousands	Sep. 30, 2017USD ($)
Commitments And Contingencies Disclosure [Abstract]
2,018	$ 57,075
2,019	46,177
2,020	37,199
2,021	30,350
2,022	23,496
Thereafter	29,257
Total minimum lease payments	$ 223,554

Commitments and Contingencies64

Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Commitments And Contingencies Disclosure [Abstract]
Operating Leases, Rent Expense, Net, Total	$ 60.1	$ 59.3	$ 39.2

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Sep. 25, 2017	Sep. 30, 2017	Sep. 30, 2016
Class Of Stock [Line Items]
Common stock (voting), shares authorized		100,000,000	100,000,000
Undesignated Preferred Stock, shares authorized		5,000,000	5,000,000
Common Stock (Voting), issued		67,700,858	59,890,885
Common Stock, Shares, outstanding		67,700,858	59,890,885
Undesignated Preferred Stock, outstanding		0	0
Net proceeds from secondary offering		$ 329,323
Common Stock [Member]
Class Of Stock [Line Items]
Issuance of common stock from secondary offering, net of issuance costs (Shares)		7,273,750
Net proceeds from secondary offering		$ 73
Allied Acquisition [Member] | Secondary Offering [Member] | Common Stock [Member]
Class Of Stock [Line Items]
Issuance of common stock in secondary offering price per share	$ 47.50
Net proceeds from secondary offering	$ 330,800

Stockholders' Equity - Reclassi

Stockholders' Equity - Reclassification out of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	$ 1,323,827	$ 883,116	$ 817,101
Other comprehensive income (loss) before reclassifications	3,706	1,024	(14,141)
Balance	1,781,806	1,323,827	883,116
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	(18,269)	(19,293)	(2,040)
Other comprehensive income (loss) before reclassifications	3,706	1,024	(14,003)
Balance	(14,563)	(18,269)	(19,293)
Derivative Financial Instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	(388)	(1,427)	(4,539)
Other comprehensive income (loss) before reclassifications			(138)
Reclassifications out of other comprehensive loss	388	1,039
Balance		(388)	(1,427)
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	(18,657)	(20,720)	(6,579)
Other comprehensive income (loss) before reclassifications	3,706	1,024	(14,141)
Reclassifications out of other comprehensive loss	388	1,039
Balance	$ (14,563)	$ (18,657)	$ (20,720)

Stock-based Compensation - Addi

Stock-based Compensation - Additional Information (Detail) - USD ($)	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Feb. 09, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation number of shares authorized			5,000,000
Stock-based compensation number of shares available for awards	4,096,732
Restricted Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares that will vest	100.00%
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non Qualified Options Expire	10 years
Allocated Share-based Compensation Expense	$ 4,800	$ 11,200
Total unrecognized compensation cost related to unvested stock	$ 4,700
Total unrecognized compensation cost related to unvested stock, expected weighted-average period of recognition	1 year 9 months 18 days
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense	$ 10,300,000	$ 6,500,000
Total unrecognized compensation cost related to unvested stock	$ 12,900,000
Total unrecognized compensation cost related to unvested stock, expected weighted-average period of recognition	1 year 9 months 18 days
Restricted Stock Units (RSUs) [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares that will vest	0.00%
Restricted Stock Units (RSUs) [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares that will vest	150.00%

Stock-based Compensation - Fair

Stock-based Compensation - Fair Values of Options, Black-Scholes Option-Pricing Model, Weighted-Average Assumptions (Detail)	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Risk-free interest rate	1.97%	1.87%	1.83%
Expected volatility	28.83%	30.96%	31.69%
Expected life (in years)	5 years 3 months 19 days	5 years 7 months 6 days	5 years 7 months 6 days
Dividend yield	0.00%	0.00%	0.00%

Stock-based compensation - Stoc

Stock-based compensation - Stock Options Outstanding and Activity During the Period (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Options Outstanding
Balance as of September 30, 2016	2,312,789
Granted	245,818
Exercised	(442,909)
Canceled/Forfeited	(16,992)
Expired	(14,478)
Balance as of September 30, 2017	2,084,228	2,312,789
Vested and expected to vest after September 30, 2017	2,050,134
Exercisable as of September 30, 2017	1,414,141
Weighted-Average Exercise Price
Beginning Balance	$ 25.55
Granted	47.40
Exercised	22.09
Canceled/Forfeited	33.72
Expired	19.50
Ending Balance	28.84	$ 25.55
Vested and expected to vest after September 30, 2017	28.74
Exercisable as of September 30, 2017	$ 25.06
Weighted-Average Remaining Contractual Life
Balance	6 years 1 month 6 days	6 years 3 months 19 days
Vested and expected to vest after September 30, 2017	6 years
Exercisable as of September 30, 2017	5 years
Aggregate Intrinsic Value
Balance	$ 46,714	$ 38,225
Vested and expected to vest after September 30, 2017	46,150
Exercisable as of September 30, 2017	$ 37,033

Stock-based compensation - St70

Stock-based compensation - Stock Option Grants, Vesting, and Exercises (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Weighted-average fair value of stock options granted	$ 14.21	$ 12.89	$ 9.40
Total fair value of stock options vested	$ 5,566	$ 12,347	$ 6,399
Total intrinsic value of stock options exercised	$ 10,941	$ 22,693	$ 4,615

Stock-based Compensation - Rest

Stock-based Compensation - Restricted Shares and Units Outstanding and Activity During the Period (Detail) - $ / shares	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Weighted - Average Grant Date Fair Value
Granted	$ 47.31	$ 38.92	$ 28.74
Restricted Stock Units (RSUs) [Member]
Outstanding
Balance at September 30, 2016	705,434
Granted	273,065
Released	(128,578)
Canceled/Forfeited	(78,948)
Balance at September 30, 2017	770,973	705,434
Vested and expected to vest after September 30, 2017	793,350
Weighted - Average Grant Date Fair Value
Balance at September 30, 2016	$ 34.55
Granted	47.31
Released	33.47
Canceled/Forfeited	29.04
Balance at September 30, 2017	38.95	$ 34.55
Vested and expected to vest after September 30, 2017	$ 38.88

Stock-based Compensation - Sche

Stock-based Compensation - Schedule Of Restricted Stock Units Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Weighted-average fair value of RSUs granted	$ 47.31	$ 38.92	$ 28.74
Total fair value of RSUs vested	$ 4,562	$ 743	$ 1,943
Total intrinsic value of RSUs released	$ 6,079	$ 1,375	$ 1,784

Income Taxes - Summary of Compo

Income Taxes - Summary of Components of Income Tax Provision (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Current:
Federal	$ 52,718	$ 23,403	$ 17,414
Foreign	1,366	1,183	1,765
State	8,975	2,426	7,579
Total current taxes	63,059	27,012	26,758
Deferred:
Federal	(656)	25,935	14,798
Foreign	0	321	(657)
State	78	3,347	2,868
Total deferred taxes	(578)	29,603	17,009
Provision for income taxes	$ 62,481	$ 56,615	$ 43,767

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Statutory Federal Income Tax Rate (Detail)	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Income Tax Disclosure [Abstract]
U.S. federal income taxes at statutory rate	35.00%	35.00%	35.00%
State income taxes, net of federal benefit	3.90%	4.20%	4.60%
Non-deductible professional fees related to RSG acquisition	0.00%	0.40%	2.20%
Other	(0.60%)	(1.00%)	(0.50%)
Effective tax rate	38.30%	38.60%	41.30%

Income Taxes - Schedule of Temp

Income Taxes - Schedule of Temporary Differences That Give Rise to Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Sep. 30, 2016
Deferred tax assets:
Deferred compensation	$ 14,237	$ 15,166
Allowance for doubtful accounts	1,318	2,060
Accrued vacation and other	6,602	6,616
Unrealized loss on financial derivatives		279
Inventory valuation	10,564	6,193
Tax loss carryforwards	20,575	34,505
Other	958	913
Total deferred tax assets	54,254	65,732
Deferred tax liabilities:
Excess tax over book depreciation and amortization	(192,637)	(201,214)
Total deferred tax liabilities	(192,637)	(201,214)
Net deferred income tax liabilities	$ (138,383)	$ (135,482)

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail)	12 Months Ended
	Sep. 30, 2017USD ($)StateProvince	Sep. 30, 2016USD ($)	Oct. 02, 2015USD ($)	Sep. 30, 2015USD ($)
Deferred Tax Assets, Operating Loss Carryforwards	$ 20,575,000	$ 34,505,000
Permanently Reinvested Foreign Earnings	44,500
Unremitted Earnings Subject to Tax If Repatriated	22,400
Goodwill	1,251,986,000	$ 1,197,565,000		$ 496,415,000
Goodwill amortizable for income tax	297,400,000
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-based Compensation Cost	34,500,000
Uncertain tax positions	$ 0
U.S. [Member]
Number of States in which Entity Operates | State	48
Canada [Member]
Number of provinces in which entity operates | Province	6
Domestic Tax Authority [Member]
Operating Loss Carryforwards			$ 135,300,000
Annual Amount of Section 382 Loss			$ 37,300,000
Net Operating Loss Carryforward Utilized	$ 37,300,000
State and Local Jurisdiction [Member]
Net Operating Loss Carryforward Utilized	$ 2,300,000

Income Taxes - Reconciliation77

Income Taxes - Reconciliation of Beginning and Ending Amounts of Gross Unrecognized Income Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Balance, beginning of year	$ 0	$ 82
Current year uncertain tax positions	0	0
Settlements	0	(82)
Balance, end of year	$ 0	$ 0

Geographic and Product Data - S

Geographic and Product Data - Schedule Of Geographic Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Segment Reporting Information [Line Items]
Net sales	$ 4,376,670	$ 4,127,109	$ 2,515,169
Long-lived assets	520,682	541,054
U.S. [Member]
Segment Reporting Information [Line Items]
Net sales	4,198,935	3,949,067	2,331,360
Long-lived assets	507,236	527,680
Canada [Member]
Segment Reporting Information [Line Items]
Net sales	177,735	178,042	$ 183,809
Long-lived assets	$ 13,446	$ 13,374

Geographic and Product Data -79

Geographic and Product Data - Schedule Of Net Sales From External Customers By Product Group (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Revenue from External Customer [Line Items]
Net sales	$ 4,376,670	$ 4,127,109	$ 2,515,169
Residential Roofing Products [Member]
Revenue from External Customer [Line Items]
Net sales	2,380,435	2,190,762	1,236,397
Non-Residential Roofing Products [Member]
Revenue from External Customer [Line Items]
Net sales	1,273,153	1,331,319	882,970
Complementary Building Products [Member]
Revenue from External Customer [Line Items]
Net sales	$ 723,082	$ 605,028	$ 395,802

Supplemental Guarantor Inform80

Supplemental Guarantor Information - Condensed Consolidated Balance Sheets (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Current assets:
Cash and cash equivalents	$ 138,250	$ 31,386	$ 45,661	$ 54,472
Accounts receivable, net	704,527	626,965
Inventories, net	551,924	480,736
Prepaid expenses and other current assets	209,138	163,103
Total current assets	1,603,839	1,302,190
Intercompany receivable, net	0	0
Investments in consolidated subsidiaries	0	0
Deferred income taxes, net	0	0	2,300
Property and equipment, net	156,129	148,569
Goodwill	1,251,986	1,197,565	496,415
Intangibles, net	429,069	464,024
Other assets, net	8,534	1,511
Total Assets	3,449,557	3,113,859
Current liabilities:
Accounts payable	503,697	360,915
Accrued expenses	261,297	161,113
Current portions of long-term debt	14,141	14,811
Total current liabilities	779,135	536,839
Intercompany payable, net	0	0
Borrowings under revolving lines of credit, net	3,205	359,661
Long-term debt, net	721,268	722,929
Deferred income taxes, net	138,383	135,482
Long-term obligations under equipment financing and other, net	25,760	35,121
Total liabilities	1,667,751	1,790,032
Total stockholders' equity	1,781,806	1,323,827	883,116	817,101
Total Liabilities and Stockholders' Equity	3,449,557	3,113,859
Parent Company [Member]
Current assets:
Cash and cash equivalents	0	0	0	0
Accounts receivable, net	0	0
Inventories, net	0	0
Prepaid expenses and other current assets	4,195	3,527
Total current assets	4,195	3,527
Intercompany receivable, net	0	0
Investments in consolidated subsidiaries	3,160,273	2,891,677
Deferred income taxes, net	30,822	59,567
Property and equipment, net	6,610	4,626
Goodwill	0	0
Intangibles, net	0	0
Other assets, net	2,912	1,242
Total Assets	3,204,812	2,960,639
Current liabilities:
Accounts payable	27,174	26,630
Accrued expenses	51,183	42,594
Current portions of long-term debt	4,500	4,500
Total current liabilities	82,857	73,724
Intercompany payable, net	618,881	840,159
Borrowings under revolving lines of credit, net	0	0
Long-term debt, net	721,268	722,929
Deferred income taxes, net	0	0
Long-term obligations under equipment financing and other, net	0	0
Total liabilities	1,423,006	1,636,812
Total stockholders' equity	1,781,806	1,323,827
Total Liabilities and Stockholders' Equity	3,204,812	2,960,639
Guarantor Subsidiaries [Member]
Current assets:
Cash and cash equivalents	149,799	37,447	42,816	58,053
Accounts receivable, net	663,034	593,395
Inventories, net	527,226	460,516
Prepaid expenses and other current assets	198,817	153,681
Total current assets	1,538,876	1,245,039
Intercompany receivable, net	655,372	878,931
Investments in consolidated subsidiaries	0	0
Deferred income taxes, net	0	0
Property and equipment, net	138,955	133,897
Goodwill	1,220,812	1,167,905
Intangibles, net	426,187	460,696
Other assets, net	5,622	269
Total Assets	3,985,824	3,886,737
Current liabilities:
Accounts payable	468,891	329,895
Accrued expenses	204,173	114,016
Current portions of long-term debt	9,641	10,311
Total current liabilities	682,705	454,222
Intercompany payable, net	0	0
Borrowings under revolving lines of credit, net	0	355,087
Long-term debt, net	0	0
Deferred income taxes, net	168,209	194,556
Long-term obligations under equipment financing and other, net	25,694	35,074
Total liabilities	876,608	1,038,939
Total stockholders' equity	3,109,216	2,847,798
Total Liabilities and Stockholders' Equity	3,985,824	3,886,737
Non-Guarantor Subsidiaries [Member]
Current assets:
Cash and cash equivalents	1,582	2,876	7,051	3,241
Accounts receivable, net	42,633	34,710
Inventories, net	24,698	20,220
Prepaid expenses and other current assets	6,126	5,895
Total current assets	75,039	63,701
Intercompany receivable, net	0	0
Investments in consolidated subsidiaries	0	0
Deferred income taxes, net	0	0
Property and equipment, net	10,564	10,046
Goodwill	31,174	29,660
Intangibles, net	2,882	3,328
Other assets, net	0	0
Total Assets	119,659	106,735
Current liabilities:
Accounts payable	21,903	14,467
Accrued expenses	5,941	4,503
Current portions of long-term debt	0	0
Total current liabilities	27,844	18,970
Intercompany payable, net	36,491	38,772
Borrowings under revolving lines of credit, net	3,205	4,574
Long-term debt, net	0	0
Deferred income taxes, net	996	493
Long-term obligations under equipment financing and other, net	66	47
Total liabilities	68,602	62,856
Total stockholders' equity	51,057	43,879
Total Liabilities and Stockholders' Equity	119,659	106,735
Eliminations and Other [Member]
Current assets:
Cash and cash equivalents	(13,131)	(8,937)	$ (4,206)	$ (6,822)
Accounts receivable, net	(1,140)	(1,140)
Inventories, net	0	0
Prepaid expenses and other current assets	0	0
Total current assets	(14,271)	(10,077)
Intercompany receivable, net	(655,372)	(878,931)
Investments in consolidated subsidiaries	(3,160,273)	(2,891,677)
Deferred income taxes, net	(30,822)	(59,567)
Property and equipment, net	0	0
Goodwill	0	0
Intangibles, net	0	0
Other assets, net	0	0
Total Assets	(3,860,738)	(3,840,252)
Current liabilities:
Accounts payable	(14,271)	(10,077)
Accrued expenses	0	0
Current portions of long-term debt	0	0
Total current liabilities	(14,271)	(10,077)
Intercompany payable, net	(655,372)	(878,931)
Borrowings under revolving lines of credit, net	0	0
Long-term debt, net	0	0
Deferred income taxes, net	(30,822)	(59,567)
Long-term obligations under equipment financing and other, net	0	0
Total liabilities	(700,465)	(948,575)
Total stockholders' equity	(3,160,273)	(2,891,677)
Total Liabilities and Stockholders' Equity	$ (3,860,738)	$ (3,840,252)

Supplemental Guarantor Inform81

Supplemental Guarantor Information - Condensed Consolidated Statements of Operations (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Net sales	$ 4,376,670	$ 4,127,109	$ 2,515,169
Cost of products sold	3,300,731	3,114,040	1,919,804
Gross profit	1,075,939	1,013,069	595,365
Operating expense	859,843	808,085	478,284
Intercompany charges (income)	0	0	0
Income from operations	216,096	204,984	117,081
Interest expense, financing costs, and other	52,751	58,452	11,037
Intercompany interest expense (income)	0	0	0
Income before provision for income taxes	163,345	146,532	106,044
Provision for (benefit from) income taxes	62,481	56,615	43,767
Income (loss) before equity in net income of subsidiaries	100,864	89,917	62,277
Equity in net income of subsidiaries	0	0	0
Net income	$ 100,864	$ 89,917	$ 62,277
Weighted-average common stock outstanding:
Basic	60,315,648	59,424,372	49,578,130
Diluted	61,344,263	60,418,067	50,173,478
Net income per share:
Basic	$ 1.67	$ 1.51	$ 1.26
Diluted	$ 1.64	$ 1.49	$ 1.24
Parent Company [Member]
Net sales	$ 0	$ 0	$ 0
Cost of products sold	0	0	0
Gross profit	0	0	0
Operating expense	28,496	59,949	44,937
Intercompany charges (income)	(4,664)	(51,942)	(36,085)
Income from operations	(23,832)	(8,007)	(8,852)
Interest expense, financing costs, and other	38,660	42,835	9,508
Intercompany interest expense (income)	(24,458)	(21,536)	(15,762)
Income before provision for income taxes	(38,034)	(29,306)	(2,598)
Provision for (benefit from) income taxes	(3,284)	(472)	(1,087)
Income (loss) before equity in net income of subsidiaries	(34,750)	(28,834)	(1,511)
Equity in net income of subsidiaries	135,614	118,751	63,788
Net income	100,864	89,917	62,277
Guarantor Subsidiaries [Member]
Net sales	4,198,935	3,949,313	2,331,829
Cost of products sold	3,162,896	2,977,174	1,778,196
Gross profit	1,036,039	972,139	553,633
Operating expense	798,328	715,669	399,901
Intercompany charges (income)	4,342	49,285	34,264
Income from operations	233,369	207,185	119,468
Interest expense, financing costs, and other	14,033	14,965	740
Intercompany interest expense (income)	22,927	19,928	14,174
Income before provision for income taxes	196,409	172,292	104,554
Provision for (benefit from) income taxes	64,399	55,613	43,765
Income (loss) before equity in net income of subsidiaries	132,010	116,679	60,789
Equity in net income of subsidiaries	0	0	0
Net income	132,010	116,679	60,789
Non-Guarantor Subsidiaries [Member]
Net sales	177,735	178,042	183,809
Cost of products sold	137,835	137,112	142,077
Gross profit	39,900	40,930	41,732
Operating expense	33,019	32,467	33,446
Intercompany charges (income)	322	2,657	1,821
Income from operations	6,559	5,806	6,465
Interest expense, financing costs, and other	58	652	789
Intercompany interest expense (income)	1,531	1,608	1,588
Income before provision for income taxes	4,970	3,546	4,088
Provision for (benefit from) income taxes	1,366	1,474	1,089
Income (loss) before equity in net income of subsidiaries	3,604	2,072	2,999
Equity in net income of subsidiaries	0	0	0
Net income	3,604	2,072	2,999
Eliminations and Other [Member]
Net sales	0	(246)	(469)
Cost of products sold	0	(246)	(469)
Gross profit	0	0	0
Operating expense	0	0	0
Intercompany charges (income)	0	0	0
Income from operations	0	0	0
Interest expense, financing costs, and other	0	0	0
Intercompany interest expense (income)	0	0	0
Income before provision for income taxes	0	0	0
Provision for (benefit from) income taxes	0	0	0
Income (loss) before equity in net income of subsidiaries	0	0	0
Equity in net income of subsidiaries	(135,614)	(118,751)	(63,788)
Net income	$ (135,614)	$ (118,751)	$ (63,788)

Supplemental Guarantor Inform82

Supplemental Guarantor Information - Condensed Consolidated Statements of Comprehensive Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Net income	$ 100,864	$ 89,917	$ 62,277
Other comprehensive income (loss):
Foreign currency translation adjustment	3,706	1,024	(14,003)
Unrealized loss due to change in fair value of derivatives, net of tax	0	0	(138)
Total other comprehensive income (loss)	3,706	1,024	(14,141)
Comprehensive income	104,570	90,941	48,136
Parent Company [Member]
Net income	100,864	89,917	62,277
Other comprehensive income (loss):
Foreign currency translation adjustment	3,706	1,024	(14,003)
Unrealized loss due to change in fair value of derivatives, net of tax			(138)
Total other comprehensive income (loss)	3,706	1,024	(14,141)
Comprehensive income	104,570	90,941	48,136
Guarantor Subsidiaries [Member]
Net income	132,010	116,679	60,789
Other comprehensive income (loss):
Foreign currency translation adjustment	0	0	0
Unrealized loss due to change in fair value of derivatives, net of tax			0
Total other comprehensive income (loss)	0	0	0
Comprehensive income	132,010	116,679	60,789
Non-Guarantor Subsidiaries [Member]
Net income	3,604	2,072	2,999
Other comprehensive income (loss):
Foreign currency translation adjustment	3,706	1,024	(14,003)
Unrealized loss due to change in fair value of derivatives, net of tax			0
Total other comprehensive income (loss)	3,706	1,024	(14,003)
Comprehensive income	7,310	3,096	(11,004)
Eliminations and Other [Member]
Net income	(135,614)	(118,751)	(63,788)
Other comprehensive income (loss):
Foreign currency translation adjustment	(3,706)	(1,024)	14,003
Unrealized loss due to change in fair value of derivatives, net of tax			0
Total other comprehensive income (loss)	(3,706)	(1,024)	14,003
Comprehensive income	$ (139,320)	$ (119,775)	$ (49,785)

Supplemental Guarantor Inform83

Supplemental Guarantor Information - Condensed Consolidated Statements of Cash Flows (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Net cash provided by (used in) operating activities	$ 315,200	$ 120,648	$ 109,340
Investing Activities
Purchases of property and equipment	(39,828)	(26,315)	(20,802)
Acquisition of businesses, net	(129,390)	(1,018,188)	(85,301)
Proceeds from the sale of assets	2,233	1,882	1,389
Intercompany activity	0	0	0
Net cash used in investing activities	(166,985)	(1,042,621)	(104,714)
Financing Activities
Borrowings under revolving lines of credit	2,464,128	1,892,459	560,634
Repayments under revolving lines of credit	(2,833,230)	(1,541,532)	(566,007)
Borrowings under term loan	0	490,793	0
Repayments under term loan	(4,500)	(230,918)	(11,250)
Repayments under equipment financing facilities and other	(10,034)	(4,724)	(5,553)
Borrowings under Senior Notes	0	300,000	0
Payment of debt issuance costs	(1,669)	(28,325)	0
Proceeds from secondary offering of common stock	345,503	0	0
Payment of issuance costs from secondary offering of common stock	(14,684)	0	0
Proceeds from issuance of common stock related to equity awards	11,341	24,160	7,943
Taxes paid related to net share settlement of equity awards	(392)	(2)	0
Excess tax benefit from stock-based compensation	2,937	4,956	1,526
Intercompany activity	0	0	0
Net cash provided by (used in) financing activities	(40,600)	906,867	(12,707)
Effect of exchange rate changes on cash and cash equivalents	(751)	831	(730)
Net increase (decrease) in cash and cash equivalents	106,864	(14,275)	(8,811)
Cash and cash equivalents, beginning of period	31,386	45,661	54,472
Cash and cash equivalents, end of period	138,250	31,386	45,661
Parent Company [Member]
Net cash provided by (used in) operating activities	(2,466)	(22,799)	1,776
Investing Activities
Purchases of property and equipment	(3,517)	(3,654)	(397)
Acquisition of businesses, net	(129,390)	(1,018,188)	(85,301)
Proceeds from the sale of assets	0	0	0
Intercompany activity	(203,163)	475,099	93,503
Net cash used in investing activities	(336,070)	(546,743)	7,805
Financing Activities
Borrowings under revolving lines of credit	0	0	552,545
Repayments under revolving lines of credit	0	0	(560,345)
Borrowings under term loan		490,793
Repayments under term loan	(4,500)	(230,918)	(11,250)
Repayments under equipment financing facilities and other	0	(45)	0
Borrowings under Senior Notes		300,000
Payment of debt issuance costs	(1,669)	(19,402)
Proceeds from secondary offering of common stock	345,503
Payment of issuance costs from secondary offering of common stock	(14,684)
Proceeds from issuance of common stock related to equity awards	11,341	24,160	7,943
Taxes paid related to net share settlement of equity awards	(392)	(2)
Excess tax benefit from stock-based compensation	2,937	4,956	1,526
Intercompany activity	0	0	0
Net cash provided by (used in) financing activities	338,536	569,542	(9,581)
Effect of exchange rate changes on cash and cash equivalents	0	0	0
Net increase (decrease) in cash and cash equivalents	0	0	0
Cash and cash equivalents, beginning of period	0	0	0
Cash and cash equivalents, end of period	0	0	0
Guarantor Subsidiaries [Member]
Net cash provided by (used in) operating activities	313,396	143,427	100,760
Investing Activities
Purchases of property and equipment	(34,584)	(20,008)	(18,649)
Acquisition of businesses, net	0	0	0
Proceeds from the sale of assets	2,150	1,882	1,389
Intercompany activity	0	0	0
Net cash used in investing activities	(32,434)	(18,126)	(17,260)
Financing Activities
Borrowings under revolving lines of credit	2,445,084	1,877,729	0
Repayments under revolving lines of credit	(2,812,663)	(1,520,003)	0
Borrowings under term loan		0
Repayments under term loan	0	0	0
Repayments under equipment financing facilities and other	(10,049)	(4,659)	(5,553)
Borrowings under Senior Notes		0
Payment of debt issuance costs	0	(8,923)
Proceeds from secondary offering of common stock	0
Payment of issuance costs from secondary offering of common stock	0
Proceeds from issuance of common stock related to equity awards	0	0	0
Taxes paid related to net share settlement of equity awards	0	0
Excess tax benefit from stock-based compensation	0	0	0
Intercompany activity	209,018	(474,814)	(93,184)
Net cash provided by (used in) financing activities	(168,610)	(130,670)	(98,737)
Effect of exchange rate changes on cash and cash equivalents	0	0	0
Net increase (decrease) in cash and cash equivalents	112,352	(5,369)	(15,237)
Cash and cash equivalents, beginning of period	37,447	42,816	58,053
Cash and cash equivalents, end of period	149,799	37,447	42,816
Non-Guarantor Subsidiaries [Member]
Net cash provided by (used in) operating activities	4,888	4,751	4,188
Investing Activities
Purchases of property and equipment	(1,727)	(2,653)	(1,756)
Acquisition of businesses, net	0	0	0
Proceeds from the sale of assets	83	0	0
Intercompany activity	0	0	0
Net cash used in investing activities	(1,644)	(2,653)	(1,756)
Financing Activities
Borrowings under revolving lines of credit	19,044	14,730	8,089
Repayments under revolving lines of credit	(20,567)	(21,529)	(5,662)
Borrowings under term loan		0
Repayments under term loan	0	0	0
Repayments under equipment financing facilities and other	15	(20)	0
Borrowings under Senior Notes		0
Payment of debt issuance costs	0	0
Proceeds from secondary offering of common stock	0
Payment of issuance costs from secondary offering of common stock	0
Proceeds from issuance of common stock related to equity awards	0	0	0
Taxes paid related to net share settlement of equity awards	0	0
Excess tax benefit from stock-based compensation	0	0	0
Intercompany activity	(2,279)	(285)	(319)
Net cash provided by (used in) financing activities	(3,787)	(7,104)	2,108
Effect of exchange rate changes on cash and cash equivalents	(751)	831	(730)
Net increase (decrease) in cash and cash equivalents	(1,294)	(4,175)	3,810
Cash and cash equivalents, beginning of period	2,876	7,051	3,241
Cash and cash equivalents, end of period	1,582	2,876	7,051
Eliminations and Other [Member]
Net cash provided by (used in) operating activities	(618)	(4,731)	2,616
Investing Activities
Purchases of property and equipment	0	0	0
Acquisition of businesses, net	0	0	0
Proceeds from the sale of assets	0	0	0
Intercompany activity	203,163	(475,099)	(93,503)
Net cash used in investing activities	203,163	(475,099)	(93,503)
Financing Activities
Borrowings under revolving lines of credit	0	0	0
Repayments under revolving lines of credit	0	0	0
Borrowings under term loan		0
Repayments under term loan	0	0	0
Repayments under equipment financing facilities and other	0	0	0
Borrowings under Senior Notes		0
Payment of debt issuance costs	0	0
Proceeds from secondary offering of common stock	0
Payment of issuance costs from secondary offering of common stock	0
Proceeds from issuance of common stock related to equity awards	0	0	0
Taxes paid related to net share settlement of equity awards	0	0
Excess tax benefit from stock-based compensation	0	0	0
Intercompany activity	(206,739)	475,099	93,503
Net cash provided by (used in) financing activities	(206,739)	475,099	93,503
Effect of exchange rate changes on cash and cash equivalents	0	0	0
Net increase (decrease) in cash and cash equivalents	(4,194)	(4,731)	2,616
Cash and cash equivalents, beginning of period	(8,937)	(4,206)	(6,822)
Cash and cash equivalents, end of period	$ (13,131)	$ (8,937)	$ (4,206)

Allowance for Doubtful Accoun84

Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Allowance For Doubtful Accounts [Abstract]
Balance at beginning of Year	$ 14,812	$ 6,298	$ 8,510
Charged to Operations	2,914	13,681	1,619
Write-offs	(5,897)	(5,167)	(3,831)
Balance at end of year	$ 11,829	$ 14,812	$ 6,298

Fair Value Measurement - Additi

Fair Value Measurement - Additional Information (Detail) - Senior Notes [Member] - USD ($) $ in Thousands		Sep. 30, 2017	Sep. 30, 2016
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Senior Notes Payable	[1]	$ 292,328	$ 291,049
Fair Value, Inputs, Level 2 [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Senior Notes Payable		300,000
Long-term Debt, Fair Value		$ 320,000
[1]	Interest rate of 6.38% as of September 30, 2017 and September 30, 2016

Employee Benefit Plans - Additi

Employee Benefit Plans - Additional Information (Details) $ in Millions	12 Months Ended
	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)	Sep. 30, 2015USD ($)
Defined Contribution Plan Service Period	90 days
Defined Contribution Plan Qualifying Age	21
Description of Defined Contribution Pension and Other Postretirement Plans	The Company currently matches the first 50% of participant contributions limited to 6% of a participant’s gross compensation (maximum Company match is 3%).
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent	100.00%
Defined Contribution Plan Minimum Annual Contributions Per Employee Percent	1.00%
Defined First 50% of Participant Contribution Plan	50.00%
Defined Contribution Plan, Cost Recognized	$ 8.2	$ 7.3	$ 4.6
Pension Contributions	$ 0.1	$ 0.1	$ 0.1
Maximum [Member]
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	6.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Match	3.00%

Financial Derivatives - Additio

Financial Derivatives - Additional Information (Details) - USD ($) $ in Millions	Mar. 31, 2017	Mar. 28, 2013	Sep. 30, 2017	Sep. 30, 2015
Derivative, Notional Amount		$ 213.8		$ 185.6
Derivative Amortizes Amount		$ 2.8
Derivative, Fair Value, Net				$ 2.4
Unrealized Gain (Loss) on Derivatives	$ 2.4
Interest Rate Swap Fixed Rate Of One Point Three Eight Percent [Member]
Derivative, Maturity Date			Mar. 31, 2017
Derivative, Fixed Interest Rate			1.38%
Derivative Amortization Frequency			quarter

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) - USD ($)	Oct. 25, 2017	Aug. 24, 2017	Sep. 30, 2017	Sep. 30, 2016
Subsequent Event [Line Items]
Preferred stock, issuance			0	0
Senior-secured Asset-based Revolving Line Of Credit [Member]
Subsequent Event [Line Items]
Long-term line of credit			$ 436,645,000	$ 796,041,000
Senior Notes [Member]
Subsequent Event [Line Items]
Debt instrument interest rate			6.38%	6.38%
Allied Acquisition [Member] | Investment Agreement [Member] | Series A Cumulative Convertible Participating Preferred Stock [Member]
Subsequent Event [Line Items]
Preferred stock, par value		$ 0.01
Preferred stock initial conversion price per share		$ 41.26
Preferred stock dividend rate		6.00%
Preferred stock, issuance		400,000
Preferred stock, liquidation preference value		$ 400,000,000
Preferred stock, liquidation purchase price per share		$ 1,000
Allied Acquisition [Member] | Subsequent Event [Member] | Secured Term Loan B Facility [Member]
Subsequent Event [Line Items]
Debt instrument maturity year	2,025
Long-term line of credit	$ 970,000,000
Debt instrument, term	7 years
Allied Acquisition [Member] | Subsequent Event [Member] | Senior-secured Asset-based Revolving Line Of Credit [Member]
Subsequent Event [Line Items]
Debt instrument maturity year	2,023
Long-term line of credit	$ 1,300,000,000
Debt instrument interest rate stated percentage on undrawn balance	0.25%
Allied Acquisition [Member] | Subsequent Event [Member] | LIBOR [Member] | Secured Term Loan B Facility [Member]
Subsequent Event [Line Items]
Debt instrument interest rate	2.25%
Allied Acquisition [Member] | Subsequent Event [Member] | LIBOR [Member] | Senior-secured Asset-based Revolving Line Of Credit [Member]
Subsequent Event [Line Items]
Debt instrument interest rate stated percentage on drawn balance	1.50%
Allied Acquisition [Member] | Senior Notes [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, aggregate principal amount	$ 1,300,000,000
Debt instrument interest rate	4.875%
Debt instrument maturity year	2,025
Allied Acquisition [Member] | Stock Purchase Agreement [Member]
Subsequent Event [Line Items]
Acquisition purchase price in cash		$ 2,625,000,000