Business and Basis of Presentation	9 Months Ended
Sep. 30, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Business and Basis of Presentation	Business and Basis of Presentation Business Foundation Building Materials (the "Company") is a specialty distributor of wallboard, suspended ceiling systems, and mechanical insulation throughout the U.S. and Canada. Based in Tustin, California, the Company employs more than 3,500 people and operates more than 220 branches across the U.S. and Canada. Organization The Company was formed on October 27, 2016 (inception). The initial stockholder of the Company was LSF9 Cypress Parent 2 LLC ("Parent 2") which held all of the Company's authorized, issued and outstanding shares of common stock. Reorganization On February 8, 2017, FBM Alpha LLC, (formerly known as LSF9 Cypress Parent, LLC) ("Alpha"), transferred its wholly owned direct subsidiary, FBM Beta LLC, (formerly known as LSF9 Cypress Holdings, LLC), and indirectly FBM Finance, Inc. to the Company, thereby transferring the business for which historical financial information is included in these results of operations, to be indirectly held by the Company (the "Reorganization"). Initial Public Offering Following the Reorganization, on February 15, 2017, the Company completed an initial public offering ("IPO") in which it issued 12,800,000 shares of common stock at a public offering price of $14.00 per share. The common stock began trading on the New York Stock Exchange on February 10, 2017 under the ticker symbol "FBM." After underwriting discounts and commissions and expenses, the net proceeds to the Company from the IPO were approximately $164.0 million. The Company used these net proceeds to repay borrowings outstanding under its asset-based revolving credit facility (the "ABL Credit Facility"). The proceeds of $164.0 million were recorded in equity, with approximately $13,000 recorded for the par value of the common stock and the remaining amount recorded in additional paid-in capital. The underwriters exercised their option to purchase an additional 1,920,000 shares of common stock from Parent 2 and those shares were purchased on February 24, 2017. The Company did not receive any proceeds from the sale of shares by Parent 2. Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States ("GAAP") for interim financial information and Article 10 of Regulation S-X. Accordingly, they do not include all the information and footnotes required by GAAP for complete financial statements. In the opinion of management, all adjustments, consisting of normal recurring adjustments necessary for a fair presentation with respect to the interim financial statements, have been included. The results of operations for interim periods are not necessarily indicative of the results for full fiscal years. For further information, refer to the consolidated financial statements and footnotes thereto for the year ended December 31, 2016, included in the Company’s Annual Report on Form 10-K filed with the Securities and Exchange Commission on March 28, 2017 (the "2016 10-K"). Principles of Consolidation The consolidated financial statements include the accounts of the Company and its consolidated subsidiaries. All intercompany balances and transactions have been eliminated. The Company has two reportable segments, Specialty Building Products ("SBP") and Mechanical Insulation ("MI"). Resources are allocated and performance is assessed by the Company's CEO, who is the Chief Operating Decision Maker ("CODM").

Business and Basis of Presentation

Business

Foundation Building Materials (the "Company") is a specialty distributor of wallboard, suspended ceiling systems, and mechanical insulation throughout the U.S. and Canada. Based in Tustin, California, the Company employs more than 3,500 people and operates more than 220 branches across the U.S. and Canada.

Organization

The Company was formed on October 27, 2016 (inception). The initial stockholder of the Company was LSF9 Cypress Parent 2 LLC ("Parent 2") which held all of the Company's authorized, issued and outstanding shares of common stock.

Reorganization

On February 8, 2017, FBM Alpha LLC, (formerly known as LSF9 Cypress Parent, LLC) ("Alpha"), transferred its wholly owned direct subsidiary, FBM Beta LLC, (formerly known as LSF9 Cypress Holdings, LLC), and indirectly FBM Finance, Inc. to the Company, thereby transferring the business for which historical financial information is included in these results of operations, to be indirectly held by the Company (the "Reorganization").

Initial Public Offering

Following the Reorganization, on February 15, 2017, the Company completed an initial public offering ("IPO") in which it issued 12,800,000 shares of common stock at a public offering price of $14.00 per share. The common stock began trading on the New York Stock Exchange on February 10, 2017 under the ticker symbol "FBM." After underwriting discounts and commissions and expenses, the net proceeds to the Company from the IPO were approximately $164.0 million. The Company used these net proceeds to repay borrowings outstanding under its asset-based revolving credit facility (the "ABL Credit Facility"). The proceeds of $164.0 million were recorded in equity, with approximately $13,000 recorded for the par value of the common stock and the remaining amount recorded in additional paid-in capital. The underwriters exercised their option to purchase an additional 1,920,000 shares of common stock from Parent 2 and those shares were purchased on February 24, 2017. The Company did not receive any proceeds from the sale of shares by Parent 2.

Basis of Presentation

The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States ("GAAP") for interim financial information and Article 10 of Regulation S-X. Accordingly, they do not include all the information and footnotes required by GAAP for complete financial statements. In the opinion of management, all adjustments, consisting of normal recurring adjustments necessary for a fair presentation with respect to the interim financial statements, have been included. The results of operations for interim periods are not necessarily indicative of the results for full fiscal years. For further information, refer to the consolidated financial statements and footnotes thereto for the year ended December 31, 2016, included in the Company’s Annual Report on Form 10-K filed with the Securities and Exchange Commission on March 28, 2017 (the "2016 10-K").

Principles of Consolidation

The consolidated financial statements include the accounts of the Company and its consolidated subsidiaries. All intercompany balances and transactions have been eliminated. The Company has two reportable segments, Specialty Building Products ("SBP") and Mechanical Insulation ("MI"). Resources are allocated and performance is assessed by the Company's CEO, who is the Chief Operating Decision Maker ("CODM").