Note 3 - Cash, Cash Equivalents and Investments (Details Textual)	6 Months Ended
Mar. 31, 2020
Maximum [Member]
Held-to-maturity Securities, Investment Term (Year)	5 years

Represents information about the Company's investment term in money market accounts and bank certificates of deposit.

No definition available.

Name:	clfd_HeldtomaturitySecuritiesInvestmentTerm
Namespace Prefix:	clfd_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration