Description of Company and Basis of Presentation	12 Months Ended
Dec. 31, 2019
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 building products distributor of wallboard, suspended ceiling systems, and metal framing throughout the United States and Canada. Based in Santa Ana, California, the Company employs more than 3,500 people and operates more than 175 branches across the United States 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"), an affiliate of Lone Star Fund IX (U.S.) L.P., which we refer to in this Annual Report on Form 10-K together with certain of its affiliates and associates (excluding us and other companies it owns as a result of its investment activities), as Lone Star. At inception, Lone Star held all of the Company's authorized, issued and outstanding shares of common stock. Principles of Consolidation The accompanying consolidated financial statements include the accounts of the Company and its consolidated subsidiaries. All intercompany balances and transactions have been eliminated. 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) ("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 ("NYSE") 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 2016 asset-based lending credit facility (the "2016 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. Secondary Public Offering On September 24, 2019, Parent 2 sold 4,750,000 shares of the Company's common stock at a price of $17.00 per share. Parent 2 also granted the underwriters an option for a period of 30 days to purchase up to an additional 712,500 shares of the Company's common stock. On October 11, 2019, the underwriters exercised their option to purchase the additional 712,500 shares of the Company's common stock. As a result of the sale, the aggregate beneficial ownership of Lone Star decreased from 65.3% to 52.5% of our outstanding shares of common stock as of December 31, 2019, and the Company remains a “Controlled Company” under the corporate governance standards of the NYSE. The Company did not receive any proceeds from the sale of the common stock by Parent 2.

Description of Company and Basis of Presentation

Description of Company

Foundation Building Materials, Inc. (the "Company") is a specialty building products distributor of wallboard, suspended ceiling systems, and metal framing throughout the United States and Canada. Based in Santa Ana, California, the Company employs more than 3,500 people and operates more than 175 branches across the United States 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"), an affiliate of Lone Star Fund IX (U.S.) L.P., which we refer to in this Annual Report on Form 10-K together with certain of its affiliates and associates (excluding us and other companies it owns as a result of its investment activities), as Lone Star. At inception, Lone Star held all of the Company's authorized, issued and outstanding shares of common stock.

Principles of Consolidation

The accompanying consolidated financial statements include the accounts of the Company and its consolidated subsidiaries. All intercompany balances and transactions have been eliminated.

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) ("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 ("NYSE") 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 2016 asset-based lending credit facility (the "2016 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.

Secondary Public Offering

On September 24, 2019, Parent 2 sold 4,750,000 shares of the Company's common stock at a price of $17.00 per share. Parent 2 also granted the underwriters an option for a period of 30 days to purchase up to an additional 712,500 shares of the Company's common stock. On October 11, 2019, the underwriters exercised their option to purchase the additional 712,500 shares of the Company's common stock. As a result of the sale, the aggregate beneficial ownership of Lone Star decreased from 65.3% to 52.5% of our outstanding shares of common stock as of December 31, 2019, and the Company remains a “Controlled Company” under the corporate governance standards of the NYSE. The Company did not receive any proceeds from the sale of the common stock by Parent 2.