Note 1 - Business and Organization (Details Textual)	3 Months Ended
	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Mar. 30, 2020 USD ($) shares	Dec. 31, 2019 USD ($)	Sep. 30, 2017
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Total	$ (2,616,000)	$ (2,749,000)
Net Cash Provided by (Used in) Operating Activities, Total	(753,000)	(869,000)
Working Capital	3,651,000
Assets, Current, Total	1,080,000			$ 1,065,000
Revenue from Contract with Customer, Including Assessed Tax	$ 439,000	$ 364,000
Number of Wholly-Owned Subsidiaries	4
BioLargo Engineering, Science & Technologies, LLC [Member]
Noncontrolling Interest, Ownership Percentage by Parent	97.50%				100.00%
Biolargo [Member] | Clyra Medical Technology Inc [Member]
Noncontrolling Interest, Ownership Percentage by Parent	36.00%			36.00%
LPC Purchase Agreement [Member]
Stock Purchase Agreement, Maximum Amount of Shares Per Day (in shares) | shares			100,000
Stock Purchase Agreement, Maximum Amount of Common Stock			$ 10,250,000
Convertible Notes, Maturing August 12 and 16, 2020 [Member]
Convertible Notes Payable, Total	$ 550,000