Note 8 - Commitments and Contingencies (Details Textual)	12 Months Ended
Dec. 31, 2018 USD ($) a	Dec. 31, 2017 USD ($)
Operating Leases, Rent Expense, Net, Total	$ 809,000	$ 755,000
Bothell, Washington Headquarters [Member]
Area of Real Estate Property \| a	32,000
Lessee, Operating Lease, Renewal Term	5 years
Monthly Base Rent Expense	$ 59,000

Term of lessee's operating lease renewal, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=77888426&loc=SL77918673-209980

Name:	us-gaap_LesseeOperatingLeaseRenewalTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant