Document And Entity Information - USD ($)	12 Months Ended
	Mar. 31, 2018	Jun. 15, 2018	Sep. 30, 2017
Document Information [Line Items]
Entity Registrant Name	Cyanotech Corp
Entity Central Index Key	0000768408
Trading Symbol	cyan
Current Fiscal Year End Date	--03-31
Entity Filer Category	Smaller Reporting Company
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	No
Entity Common Stock, Shares Outstanding (in shares)		5,772,032
Entity Public Float			$ 18,602,266
Document Type	10-K
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Amendment Flag	false