Basis of Presentation	9 Months Ended
Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation As previously disclosed, on June 18, 2017 (the "Petition Date"), A. M. Castle & Co. (the "Company") and four of its subsidiaries (together with the Company, the "Debtors") filed voluntary petitions for reorganization under chapter 11 of the United States Bankruptcy Code (the "Bankruptcy Code") with the United States Bankruptcy Court for the District of Delaware in Wilmington, Delaware (the "Bankruptcy Court"). Also on June 18, 2017, the Debtors filed the Debtors' Prepackaged Joint Chapter 11 Plan of Reorganization with the Bankruptcy Court and on July 25, 2017, the Debtors filed the Debtors' Amended Prepackaged Joint Chapter 11 Plan of Reorganization (the "Plan") with the Bankruptcy Court. On August 2, 2017, the Bankruptcy Court entered an order (the "Confirmation Order") confirming the Plan. On August 31, 2017 (the "Effective Date"), the Plan became effective pursuant to its terms and the Debtors emerged from their chapter 11 cases. Refer to Note 2 - Bankruptcy Related Disclosures. The Condensed Consolidated Financial Statements included herein have been prepared to reflect the application of Financial Accounting Standards Board ("FASB") Accounting Standards Codification ("ASC") No. 852, "Reorganizations" and ASC 805, "Business Combinations". Accordingly, the Company adopted fresh-start accounting upon emergence from their chapter 11 cases and became a new entity for financial reporting purposes as of September 1, 2017. For accounting purposes all emergence related transactions of the Predecessor including the impact of the issuance of the Successor common stock, the entry into a new asset-based revolving credit facility and new senior secured convertible notes, and the accelerated debt obligations of the Company that were satisfied pursuant to the terms of the Plan, were recorded as of August 31, 2017. Accordingly, the Condensed Consolidated Financial Statements for the Successor are not comparable to the Condensed Consolidated Financial Statements for the Predecessor. Also in connection with the adoption of fresh-start accounting, the Company elected to make an accounting policy change related to the accounting for stock-based compensation. The Predecessor estimated the level of forfeitures expected to occur at the time of each grant and recorded compensation expense only for those stock-based awards that it ultimately expected would vest. The estimate was based on the Company's historical rates of forfeitures and was updated periodically. The Successor has elected to no longer estimate the number of stock-based awards expected to vest but rather, will account for forfeitures as they occur. The Condensed Consolidated Financial Statements included herein have been prepared by the Company, without audit, pursuant to the rules and regulations of the U.S. Securities and Exchange Commission (“SEC”), and accounting principles generally accepted in the United States of America (“GAAP”). This report contains Condensed Consolidated Financial Statements of the Company as of September 30, 2018 (Successor) and for the three and nine months ended September 30, 2018 (Successor), for the period from July 1, 2017 to August 31, 2017 (Predecessor), for the period from January 1, 2017 to August 31, 2017 (Predecessor), and for the period from September 1, 2017 to September 30, 2017 (Successor). The Condensed Consolidated Balance Sheet at December 31, 2017 (Successor) is derived from the audited financial statements at that date. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to the rules and regulations of the SEC. In the opinion of management, the unaudited statements included herein contain all adjustments (consisting of only normal recurring adjustments) necessary for a fair presentation of financial results for the interim period. These Condensed Consolidated Financial Statements should be read in conjunction with the Consolidated Financial Statements and the Notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017. The 2018 interim results reported herein may not necessarily be indicative of the results of the Company’s operations for the full year.

Basis of Presentation

As previously disclosed, on June 18, 2017 (the "Petition Date"), A. M. Castle & Co. (the "Company") and four of its subsidiaries (together with the Company, the "Debtors") filed voluntary petitions for reorganization under chapter 11 of the United States Bankruptcy Code (the "Bankruptcy Code") with the United States Bankruptcy Court for the District of Delaware in Wilmington, Delaware (the "Bankruptcy Court"). Also on June 18, 2017, the Debtors filed the Debtors' Prepackaged Joint Chapter 11 Plan of Reorganization with the Bankruptcy Court and on July 25, 2017, the Debtors filed the Debtors' Amended Prepackaged Joint Chapter 11 Plan of Reorganization (the "Plan") with the Bankruptcy Court. On August 2, 2017, the Bankruptcy Court entered an order (the "Confirmation Order") confirming the Plan. On August 31, 2017 (the "Effective Date"), the Plan became effective pursuant to its terms and the Debtors emerged from their chapter 11 cases. Refer to Note 2 - Bankruptcy Related Disclosures.

The Condensed Consolidated Financial Statements included herein have been prepared to reflect the application of Financial Accounting Standards Board ("FASB") Accounting Standards Codification ("ASC") No. 852, "Reorganizations" and ASC 805, "Business Combinations". Accordingly, the Company adopted fresh-start accounting upon emergence from their chapter 11 cases and became a new entity for financial reporting purposes as of September 1, 2017. For accounting purposes all emergence related transactions of the Predecessor including the impact of the issuance of the Successor common stock, the entry into a new asset-based revolving credit facility and new senior secured convertible notes, and the accelerated debt obligations of the Company that were satisfied pursuant to the terms of the Plan, were recorded as of August 31, 2017. Accordingly, the Condensed Consolidated Financial Statements for the Successor are not comparable to the Condensed Consolidated Financial Statements for the Predecessor.

Also in connection with the adoption of fresh-start accounting, the Company elected to make an accounting policy change related to the accounting for stock-based compensation. The Predecessor estimated the level of forfeitures expected to occur at the time of each grant and recorded compensation expense only for those stock-based awards that it ultimately expected would vest. The estimate was based on the Company's historical rates of forfeitures and was updated periodically. The Successor has elected to no longer estimate the number of stock-based awards expected to vest but rather, will account for forfeitures as they occur.

The Condensed Consolidated Financial Statements included herein have been prepared by the Company, without audit, pursuant to the rules and regulations of the U.S. Securities and Exchange Commission (“SEC”), and accounting principles generally accepted in the United States of America (“GAAP”). This report contains Condensed Consolidated Financial Statements of the Company as of September 30, 2018 (Successor) and for the three and nine months ended September 30, 2018 (Successor), for the period from July 1, 2017 to August 31, 2017 (Predecessor), for the period from January 1, 2017 to August 31, 2017 (Predecessor), and for the period from September 1, 2017 to September 30, 2017 (Successor). The Condensed Consolidated Balance Sheet at December 31, 2017 (Successor) is derived from the audited financial statements at that date. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to the rules and regulations of the SEC. In the opinion of management, the unaudited statements included herein contain all adjustments (consisting of only normal recurring adjustments) necessary for a fair presentation of financial results for the interim period. These Condensed Consolidated Financial Statements should be read in conjunction with the Consolidated Financial Statements and the Notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017. The 2018 interim results reported herein may not necessarily be indicative of the results of the Company’s operations for the full year.