Note 9 - Commitments and Contingencies (Details Textual) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jul. 01, 2018
Operating Leases, Rent Expense, Net, Total	$ 700	$ 600	$ 1,300	$ 1,100
Operating Leases, Future Minimum Payments Due, Total	10,015		10,015
Purchase Obligation, Due in Next Twelve Months	13,700		13,700
Loss Contingency Accrual, Ending Balance	$ 0		$ 0
Lease in Santa Clara, California [Member] | Subsequent Event [Member]
Lessee, Operating Lease, Term of Contract					10 years
Operating Leases, Future Minimum Payments Due, Total					$ 7,000
Operating Lease, Abatement Allowance					400
Operating Lease, Tenant Improvement Allowance					$ 1,300