Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2021	May 03, 2021
Document Information [Line Items]
Entity Registrant Name	LGL GROUP INC
Entity Central Index Key	0000061004
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		5,272,204
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2021
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity File Number	001-00106
Entity Tax Identification Number	38-1799862
Entity Address, Address Line One	2525 Shader Rd
Entity Address, City or Town	Orlando
Entity Address, State or Province	FL
Entity Address, Postal Zip Code	32804
City Area Code	407
Local Phone Number	298-2000
Entity Incorporation, State or Country Code	DE
Document Quarterly Report	true
Document Transition Report	false
Entity Interactive Data Current	Yes
Common Stock [Member]
Document Information [Line Items]
Trading Symbol	LGL
Title of 12(b) Security	Common Stock, par value $0.01
Security Exchange Name	NYSE
Warrants To Purchase Common Stock [Member]
Document Information [Line Items]
Trading Symbol	LGL WS
Title of 12(b) Security	Warrants to Purchase Common Stock, par value $0.01
Security Exchange Name	NYSE