Organization and Basis of Presentation (Policies)	6 Months Ended
Jun. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization	Organization. We (NYSE American: CIX) are 86% owned by NL Industries, Inc. (NYSE: NL) at June 30, 2019. We manufacture and sell component products (security products and recreational marine components). At June 30, 2019, Valhi, Inc. (NYSE: VHI) owns 83% of NL’s outstanding common stock and a wholly-owned subsidiary of Contran Corporation owns 92% of Valhi’s outstanding common stock. At June 30, 2019, all of Contran’s outstanding voting stock was held by a family trust established for the benefit of Lisa K. Simmons and Serena Simmons Connelly and their children, for which Ms. Simmons and Ms. Connelly were co-trustees (the “Family Trust”), or was held directly by Ms. Simmons and Ms. Connelly or various other family trusts established for the benefit of Ms. Simmons and Ms. Connelly and their children and for which Ms. Simmons or Ms. Connelly, applicable, serve as trustee (collectively, the “Other Trusts”). Consequently, at June 30, 2019, Ms. Simmons and Ms. Connelly may be deemed to control Contran, Valhi, NL and us. Effective July 16, 2019, and upon entry of an agreed final judgment by the probate court of Dallas County in the state of Texas, Ms. Simmons and Ms. Connelly appointed two third parties as successor co-trustees of the Family Trust. Ms. Simmons and Ms. Connelly retain the ability to appoint qualifying successor trustees of the Family Trust if either or both of the third party successor trustees resign or otherwise do not serve as trustee. Following such appointment, a majority of Contran’s outstanding voting stock is held directly by Ms. Simmons and Ms. Connelly and the Other Trusts and the remainder of Contran’s outstanding voting stock is held by the Family Trust. Consequently, as of July 16, 2019, Ms. Simmons and Ms. Connelly and the trustees of the Family Trust may be deemed to control Contran and us.
Basis of Presentation	Basis of presentation. Consolidated in this Quarterly Report are the results of CompX International Inc. and its subsidiaries. The unaudited Condensed Consolidated Financial Statements contained in this Quarterly Report have been prepared on the same basis as the audited Consolidated Financial Statements included in our Annual Report on Form 10-K for the year ended December 31, 2018 that we filed with the Securities and Exchange Commission (“SEC”) on February 27, 2019 (the “2018 Annual Report”). In our opinion, we have made all necessary adjustments (which include only normal recurring adjustments) in order to state fairly, in all material respects, our consolidated financial position, results of operations and cash flows as of the dates and for the periods presented. We have condensed the Consolidated Balance Sheet at December 31, 2018 contained in this Quarterly Report as compared to our audited Consolidated Financial Statements at that date, and we have omitted certain information and footnote disclosures (including those related to the Consolidated Balance Sheet at December 31, 2018) normally included in financial statements prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”). Our results of operations for the interim periods ended June 30, 2019 may not be indicative of our operating results for the full year. The Condensed Consolidated Financial Statements contained in this Quarterly Report should be read in conjunction with our 2018 Consolidated Financial Statements contained in our 2018 Annual Report. Our operations are reported on a 52 or 53-week year. For presentation purposes, annual and quarterly information in the Condensed Consolidated Financial Statements and accompanying notes are presented as ended June 30, 2018, December 31, 2018 and June 30, 2019. The actual dates of our annual and quarterly periods are July 1, 2018, December 30, 2018 and June 30, 2019, respectively. Unless otherwise indicated, references in this report to “we”, “us” or “our” refer to CompX International Inc. and its subsidiaries, taken as a whole.

Organization and Basis of Presentation (Policies)

6 Months Ended

Jun. 30, 2019

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Organization. We (NYSE American: CIX) are 86% owned by NL Industries, Inc. (NYSE: NL) at June 30, 2019. We manufacture and sell component products (security products and recreational marine components). At June 30, 2019, Valhi, Inc. (NYSE: VHI) owns 83% of NL’s outstanding common stock and a wholly-owned subsidiary of Contran Corporation owns 92% of Valhi’s outstanding common stock. At June 30, 2019, all of Contran’s outstanding voting stock was held by a family trust established for the benefit of Lisa K. Simmons and Serena Simmons Connelly and their children, for which Ms. Simmons and Ms. Connelly were co-trustees (the “Family Trust”), or was held directly by Ms. Simmons and Ms. Connelly or various other family trusts established for the benefit of Ms. Simmons and Ms. Connelly and their children and for which Ms. Simmons or Ms. Connelly, applicable, serve as trustee (collectively, the “Other Trusts”). Consequently, at June 30, 2019, Ms. Simmons and Ms. Connelly may be deemed to control Contran, Valhi, NL and us.

Effective July 16, 2019, and upon entry of an agreed final judgment by the probate court of Dallas County in the state of Texas, Ms. Simmons and Ms. Connelly appointed two third parties as successor co-trustees of the Family Trust. Ms. Simmons and Ms. Connelly retain the ability to appoint qualifying successor trustees of the Family Trust if either or both of the third party successor trustees resign or otherwise do not serve as trustee. Following such appointment, a majority of Contran’s outstanding voting stock is held directly by Ms. Simmons and Ms. Connelly and the Other Trusts and the remainder of Contran’s outstanding voting stock is held by the Family Trust. Consequently, as of July 16, 2019, Ms. Simmons and Ms. Connelly and the trustees of the Family Trust may be deemed to control Contran and us.

Basis of Presentation

Basis of presentation. Consolidated in this Quarterly Report are the results of CompX International Inc. and its subsidiaries. The unaudited Condensed Consolidated Financial Statements contained in this Quarterly Report have been prepared on the same basis as the audited Consolidated Financial Statements included in our Annual Report on Form 10-K for the year ended December 31, 2018 that we filed with the Securities and Exchange Commission (“SEC”) on February 27, 2019 (the “2018 Annual Report”). In our opinion, we have made all necessary adjustments (which include only normal recurring adjustments) in order to state fairly, in all material respects, our consolidated financial position, results of operations and cash flows as of the dates and for the periods presented. We have condensed the Consolidated Balance Sheet at December 31, 2018 contained in this Quarterly Report as compared to our audited Consolidated Financial Statements at that date, and we have omitted certain information and footnote disclosures (including those related to the Consolidated Balance Sheet at December 31, 2018) normally included in financial statements prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”). Our results of operations for the interim periods ended June 30, 2019 may not be indicative of our operating results for the full year. The Condensed Consolidated Financial Statements contained in this Quarterly Report should be read in conjunction with our 2018 Consolidated Financial Statements contained in our 2018 Annual Report.

Our operations are reported on a 52 or 53-week year. For presentation purposes, annual and quarterly information in the Condensed Consolidated Financial Statements and accompanying notes are presented as ended June 30, 2018, December 31, 2018 and June 30, 2019. The actual dates of our annual and quarterly periods are July 1, 2018, December 30, 2018 and June 30, 2019, respectively. Unless otherwise indicated, references in this report to “we”, “us” or “our” refer to CompX International Inc. and its subsidiaries, taken as a whole.