Basis of Presentation	12 Months Ended
Dec. 31, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Basis of Presentation	A. Basis of Presentation The consolidated financial statements include the accounts of The LGL Group, Inc. (the “Company”, “we”, “our” or “us”) and all of its majority-owned subsidiaries except its sole variable interest entity (“VIE”), LGL Systems Acquisition Holding Company, LLC. Intercompany transactions and accounts have been eliminated in consolidation. These consolidated financial statements and accompanying notes have been prepared in accordance with accounting principles generally accepted in the United States (“GAAP”). Certain amounts in prior years’ consolidated financial statements have been reclassified to conform to the current year presentation. The Company was incorporated in 1928 under the laws of the State of Indiana and reincorporated under the laws of the State of Delaware in 2007, and is a diversified holding company with subsidiaries engaged in the design, manufacturing and marketing of highly-engineered, high reliability frequency and spectrum control products used to control the frequency or timing of signals in electronic circuits and in the design of high performance Frequency and Time Reference Standards that form the basis for timing and synchronization in various applications. The Company operates through its two principal subsidiaries, (1) M-tron Industries, Inc. ("MtronPTI"), which includes the operations of Piezo Technology, Inc. ("PTI") and M-tron Asia, LLC ("Mtron"), and (2) Precise Time and Frequency, LLC ("PTF"). The Company has operations in Orlando, Florida; Yankton, South Dakota; Wakefield, Massachusetts; and Noida, India. MtronPTI also has sales offices in Austin, Texas and Hong Kong. In 2019, the Company created an intermediate holding company, M-tron Systems Holdings, LLC, for its existing operating assets and reorganized to facilitate opportunities to further diversify its portfolio. The Company formed three subsidiaries: M-tron Systems Holdings, LLC, LGL Systems Acquisition Holding Company, LLC and LGL Systems Acquisition Corp. LGL Systems Acquisition Holding Company, LLC (the “Sponsor”) is the sponsor of LGL Systems Acquisition Corp., a special purpose acquisition company, commonly referred to as a “SPAC” or blank check company, formed for the purpose of effecting a business combination in the aerospace, defense and communications industries (the “SPAC”). The SPAC is listed on the NYSE American under the ticker symbol “DFNS.” See Note C - Equity Investment in Unconsolidated Subsidiary.

Basis of Presentation

12 Months Ended

Dec. 31, 2020

Organization Consolidation And Presentation Of Financial Statements [Abstract]

A. Basis of Presentation

The consolidated financial statements include the accounts of The LGL Group, Inc. (the “Company”, “we”, “our” or “us”) and all of its majority-owned subsidiaries except its sole variable interest entity (“VIE”), LGL Systems Acquisition Holding Company, LLC. Intercompany transactions and accounts have been eliminated in consolidation. These consolidated financial statements and accompanying notes have been prepared in accordance with accounting principles generally accepted in the United States (“GAAP”).

Certain amounts in prior years’ consolidated financial statements have been reclassified to conform to the current year presentation.

The Company was incorporated in 1928 under the laws of the State of Indiana and reincorporated under the laws of the State of Delaware in 2007, and is a diversified holding company with subsidiaries engaged in the design, manufacturing and marketing of highly-engineered, high reliability frequency and spectrum control products used to control the frequency or timing of signals in electronic circuits and in the design of high performance Frequency and Time Reference Standards that form the basis for timing and synchronization in various applications.

The Company operates through its two principal subsidiaries, (1) M-tron Industries, Inc. ("MtronPTI"), which includes the operations of Piezo Technology, Inc. ("PTI") and M-tron Asia, LLC ("Mtron"), and (2) Precise Time and Frequency, LLC ("PTF"). The Company has operations in Orlando, Florida; Yankton, South Dakota; Wakefield, Massachusetts; and Noida, India. MtronPTI also has sales offices in Austin, Texas and Hong Kong.

In 2019, the Company created an intermediate holding company, M-tron Systems Holdings, LLC, for its existing operating assets and reorganized to facilitate opportunities to further diversify its portfolio. The Company formed three subsidiaries: M-tron Systems Holdings, LLC, LGL Systems Acquisition Holding Company, LLC and LGL Systems Acquisition Corp. LGL Systems Acquisition Holding Company, LLC (the “Sponsor”) is the sponsor of LGL Systems Acquisition Corp., a special purpose acquisition company, commonly referred to as a “SPAC” or blank check company, formed for the purpose of effecting a business combination in the aerospace, defense and communications industries (the “SPAC”). The SPAC is listed on the NYSE American under the ticker symbol “DFNS.” See Note C - Equity Investment in Unconsolidated Subsidiary.