Note 12 - Stockholders' Equity - Number of Shares Available for Future Issuance (Details)	Dec. 31, 2017 shares
Preferred shares available for future issuance (in shares)	5,000,000
Common and preferred shares available for future issuance (in shares)	6,412,000
1993 Employee Stock Purchase Plan (ESPP) [Member]
Common shares available for future issuance (in shares)	715,000
Incentive Plans Excluding ESPP [Member]
Common shares available for future issuance (in shares)	697,000