Equity Investment in Unconsolidated Subsidiary	12 Months Ended
Dec. 31, 2020
Equity Method Investments And Joint Ventures [Abstract]
Equity Investment in Unconsolidated Subsidiary	C. Equity Investment in Unconsolidated Subsidiary On November 6, 2019, the Company invested $3.35 million in LGL Systems Acquisition Holding Company, LLC, a partially owned subsidiary that serves as the Sponsor of the SPAC. The SPAC is a publicly-traded company on the NYSE American under the ticker symbol “DFNS” which was formed for the purpose of effecting a business combination in the aerospace, defense and communications industries. The Sponsor holds 100% of the SPAC’s Class B common shares, which are restricted and non-tradable and 5,200,000 private warrants. The Sponsor purchased the private warrants in a private placement that closed simultaneously with the consummation of the SPAC’s initial public offering (“SPAC IPO”). Each private warrant is exercisable to purchase one share of common stock of the SPAC at an exercise price of $11.50 per share. The Company contributed 62.2% of the Sponsor’s risk capital to effect the SPAC IPO. The SPAC IPO closed on November 12, 2019; proceeds from the SPAC IPO totaled $172.5 million. If the SPAC does not complete a business combination within 24 months from the closing of the SPAC IPO, the proceeds from the sale of the private warrants will be used to fund the redemption of the shares sold in the SPAC IPO (subject to the requirements of applicable law); and the private warrants will expire worthless. The Sponsor holds 20% of the total common shares (Class A and Class B) in the SPAC along with the 5,200,000 private warrants. (See Note Q – Subsequent Event.) The Sponsor is managed by LGL Systems Nevada Management Partners LLC (“Nevada GP”), an affiliated entity deemed to be under the significant influence of Marc Gabelli, the Company’s Chairman of the Board. The Company has determined that it is not the primary beneficiary of the Sponsor, as Nevada GP has the power to direct the activities of the Sponsor that most significantly impact the Sponsor’s economic performance through an operating agreement. The Company, therefore, accounts for the Sponsor under the equity method of accounting. For the years ended December 31, 2020 and 2019, the Company recognized a loss on equity investment in unconsolidated subsidiary of $262,000 and $16,000, respectively. The Company has recognized a cumulative loss of $278,000 on its investment in the unconsolidated Sponsor as December 31, 2020.

Equity Investment in Unconsolidated Subsidiary

12 Months Ended

Dec. 31, 2020

Equity Method Investments And Joint Ventures [Abstract]

Equity Investment in Unconsolidated Subsidiary

C. Equity Investment in Unconsolidated Subsidiary

On November 6, 2019, the Company invested $3.35 million in LGL Systems Acquisition Holding Company, LLC, a partially owned subsidiary that serves as the Sponsor of the SPAC. The SPAC is a publicly-traded company on the NYSE American under the ticker symbol “DFNS” which was formed for the purpose of effecting a business combination in the aerospace, defense and communications industries. The Sponsor holds 100% of the SPAC’s Class B common shares, which are restricted and non-tradable and 5,200,000 private warrants. The Sponsor purchased the private warrants in a private placement that closed simultaneously with the consummation of the SPAC’s initial public offering (“SPAC IPO”). Each private warrant is exercisable to purchase one share of common stock of the SPAC at an exercise price of $11.50 per share. The Company contributed 62.2% of the Sponsor’s risk capital to effect the SPAC IPO.

The SPAC IPO closed on November 12, 2019; proceeds from the SPAC IPO totaled $172.5 million. If the SPAC does not complete a business combination within 24 months from the closing of the SPAC IPO, the proceeds from the sale of the private warrants will be used to fund the redemption of the shares sold in the SPAC IPO (subject to the requirements of applicable law); and the private warrants will expire worthless. The Sponsor holds 20% of the total common shares (Class A and Class B) in the SPAC along with the 5,200,000 private warrants. (See Note Q – Subsequent Event.)

The Sponsor is managed by LGL Systems Nevada Management Partners LLC (“Nevada GP”), an affiliated entity deemed to be under the significant influence of Marc Gabelli, the Company’s Chairman of the Board. The Company has determined that it is not the primary beneficiary of the Sponsor, as Nevada GP has the power to direct the activities of the Sponsor that most significantly impact the Sponsor’s economic performance through an operating agreement. The Company, therefore, accounts for the Sponsor under the equity method of accounting. For the years ended December 31, 2020 and 2019, the Company recognized a loss on equity investment in unconsolidated subsidiary of $262,000 and $16,000, respectively. The Company has recognized a cumulative loss of $278,000 on its investment in the unconsolidated Sponsor as December 31, 2020.