Note 7 - Commitments and Contingencies (Details Textual)	3 Months Ended
	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)	Feb. 01, 2017 USD ($) ft² $ / item
Operating Leases, Rent Expense, Total | $	$ 138,000	$ 73,000
Sublease Agreement for Relocation of Headquarters [Member]
Area of Real Estate Property | ft²			12,400
Operating Leases, Monthly Rent Per Rentable Square Foot During First Year | $ / item			20.5
Operating Leases, Monthly Rent Per Rentable Square Foot During Second Year | $ / item			21.12
Operating Leases, Monthly Rent Per Rentable Square Foot During Third Year | $ / item			21.75
Security Deposit | $			$ 22,000
Operating Leases, Allowance for Certain Improvements | $			$ 88,000