Description of Company and Basis of Presentation	12 Months Ended
Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Company and Basis of Presentation	Description of Company and Basis of Presentation Description of Company Foundation Building Materials, Inc. (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 3,700 people and operates more than 200 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. Parent 2 is controlled by investment funds, or affiliates of investment funds, advised, managed or controlled by Lone Star Fund IX (U.S.) L. P., (together with certain of its affiliates and associates, but excluding the Company and other companies it owns as a result of its investment activities, “Lone Star”). Principles of Consolidation The consolidated financial statements of the Successor and Predecessor include the accounts of the Company and its consolidated subsidiaries. All intercompany balances and transactions have been eliminated. The Company reports two reportable segments, Specialty Building Products and Mechanical Insulation. Resources are allocated and performance is assessed by the Company's CEO, who is the Chief Operating Decision Maker ("CODM"). Basis of Presentation The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America ("GAAP"). 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), 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"). As a result of the Reorganization, the historical share count information reflected in the Consolidated Statement of Changes in Stockholders' Equity reflects a 29,974.239 to 1 stock split with respect to the common stock of the Company that occurred subsequent to December 31, 2016. The stock split is reflected as if it occurred at the beginning of the Successor period. Initial Public Offering Following the Reorganization, on February 15, 2017, FBM 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 estimated expenses, the net proceeds to the Company from the IPO were approximately $164.0 million. the Company used these net proceeds to repay $164.0 million of borrowings outstanding under the asset-based lending credit facility (the "ABL Credit Facility"). 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.

Description of Company and Basis of Presentation

Description of Company

Foundation Building Materials, Inc. (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 3,700 people and operates more than 200 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. Parent 2 is controlled by investment funds, or affiliates of investment funds, advised, managed or controlled by Lone Star Fund IX (U.S.) L. P., (together with certain of its affiliates and associates, but excluding the Company and other companies it owns as a result of its investment activities, “Lone Star”).

Principles of Consolidation

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

Basis of Presentation

The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America ("GAAP").

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), 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"). As a result of the Reorganization, the historical share count information reflected in the Consolidated Statement of Changes in Stockholders' Equity reflects a 29,974.239 to 1 stock split with respect to the common stock of the Company that occurred subsequent to December 31, 2016. The stock split is reflected as if it occurred at the beginning of the Successor period.

Initial Public Offering

Following the Reorganization, on February 15, 2017, FBM 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 estimated expenses, the net proceeds to the Company from the IPO were approximately $164.0 million. the Company used these net proceeds to repay $164.0 million of borrowings outstanding under the asset-based lending credit facility (the "ABL Credit Facility"). 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.