Document and Entity Information - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Mar. 24, 2021	Jun. 30, 2020
Document and Entity Information [Abstract]
Entity Registrant Name	BLONDER TONGUE LABORATORIES INC
Entity Central Index Key	0001000683
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Type	10-K
Document Period End Date	Dec. 31, 2020
Document Fiscal Period Focus	FY
Document Fiscal Year Focus	2020
Entity Current Reporting Status	Yes
Entity Well Known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Filer Category	Non-accelerated Filer
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		11,874,045
Entity File Number	1-14120
Entity Interactive Data Current	Yes
Entity Incorporation State Country Code	DE
Entity Public Float			$ 3,323,352