Business and Basis of Presentation	9 Months Ended
Sep. 30, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Business and Basis of Presentation	1. Business and Basis of Presentation Business Foundation Building Materials, Inc. (the "Company"), based in Tustin, California is a specialty distributor of wallboard, suspended ceiling systems, and metal framing throughout the U.S. and Canada. On September 26, 2018, the Company entered into a definitive agreement to sell its mechanical insulation business. Refer to Note 3, Discontinued Operations, for further details. Excluding its mechanical insulation business, the Company employs more than 3,400 people and operates more than 170 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, Foundation Building Materials Holding Company LLC (formerly known as FBM Beta LLC and LSF9 Cypress Holdings, LLC) ("Holdco"), 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 then-existing asset-based revolving credit facility (the "2016 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, 2017, included in the Company’s Annual Report on Form 10-K filed with the Securities and Exchange Commission on February 27, 2018 (the "2017 10-K"), which do not include the discontinued operations from the sale of the mechanical insulation segment. The Company plans to retrospectively adjust previously reported audited financial statements to recognize the discontinued operations for the sale of the mechanical insulation segment when it files its 2018 10-K in 2019. When the sale of the mechanical insulation segment closes, the Company will file a Current Report on Form 8-K with pro forma financial statements that will include full year 2016 and 2017 statements of operations. As discussed in Note 3, Discontinued Operations, the Company has entered into a definitive agreement to sell its mechanical insulation business, which was previously reported as the mechanical insulation segment. The previously reported amounts for the mechanical insulation segment have been reclassified to discontinued operations for all periods presented. The Company’s continuing operations now consist of what was previously reported as the Specialty Building Products segment for all periods presented 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.

1. Business and Basis of Presentation

Business

Foundation Building Materials, Inc. (the "Company"), based in Tustin, California is a specialty distributor of wallboard, suspended ceiling systems, and metal framing throughout the U.S. and Canada.

On September 26, 2018, the Company entered into a definitive agreement to sell its mechanical insulation business. Refer to Note 3, Discontinued Operations, for further details. Excluding its mechanical insulation business, the Company employs more than 3,400 people and operates more than 170 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, Foundation Building Materials Holding Company LLC (formerly known as FBM Beta LLC and LSF9 Cypress Holdings, LLC) ("Holdco"), 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 then-existing asset-based revolving credit facility (the "2016 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, 2017, included in the Company’s Annual Report on Form 10-K filed with the Securities and Exchange Commission on February 27, 2018 (the "2017 10-K"), which do not include the discontinued operations from the sale of the mechanical insulation segment. The Company plans to retrospectively adjust previously reported audited financial statements to recognize the discontinued operations for the sale of the mechanical insulation segment when it files its 2018 10-K in 2019. When the sale of the mechanical insulation segment closes, the Company will file a Current Report on Form 8-K with pro forma financial statements that will include full year 2016 and 2017 statements of operations.

As discussed in Note 3, Discontinued Operations, the Company has entered into a definitive agreement to sell its mechanical insulation business, which was previously reported as the mechanical insulation segment. The previously reported amounts for the mechanical insulation segment have been reclassified to discontinued operations for all periods presented. The Company’s continuing operations now consist of what was previously reported as the Specialty Building Products segment for all periods presented

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.