Note 1 - Summary of Significant Accounting Policies - Effect of Adoption of the New Standard (Details) - USD ($)		3 Months Ended								12 Months Ended
		Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2017	Jan. 01, 2019		Jan. 01, 2018
Other long-term assets		$ 6,411,000				$ 5,971,000				$ 6,411,000	$ 5,971,000
Deferred revenue						12,566,000					12,566,000
Retained earnings (deficit)		(36,358,000)				(24,010,000)				(36,358,000)	(24,010,000)
Products revenue										181,712,000	162,720,000		$ 151,493,000
Sales and marketing		20,323,000	$ 17,691,000	$ 16,992,000	$ 16,104,000	15,318,000	$ 14,479,000	$ 15,535,000	$ 13,088,000	71,109,000	58,420,000		52,070,000
Interest and other income, net*		(20,000)	$ (146,000)	$ 46,000	$ (79,000)	(44,000)	$ (49,000)	$ (129,000)	$ 98,000	(199,000)	(123,000)	[1]	884,000
Operating Lease, Right-of-Use Asset		7,702,000								7,702,000				$ 10,049,000
Operating lease liabilities		(2,800,000)								(2,800,000)				(2,430,000)
Other long-term liabilities*		578,000				553,000				578,000	553,000				[1]
Operating lease liabilities, net of current portion		$ (5,112,000)								(5,112,000)				(7,759,000)
Accounting Standards Update 2016-02 [Member]
Operating Lease, Right-of-Use Asset														(10,049,000)
Operating lease liabilities														2,430,000
Other long-term liabilities*	[1]													140,000
Operating lease liabilities, net of current portion														$ 7,759,000
Previous Accounting Guidance [Member]
Operating Lease, Right-of-Use Asset
Operating lease liabilities
Other long-term liabilities*	[1]					140,000					140,000
Operating lease liabilities, net of current portion
Accounting Standards Update 2014-09 [Member]
Deferred revenue																$ (237,000)
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Other long-term assets						(5,217,000)					(5,217,000)
Deferred revenue						(106,000)					(106,000)
Retained earnings (deficit)						4,610,000					4,610,000
Interest and other income, net*	[1]										297,000
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Other long-term assets						754,000					754,000
Deferred revenue						12,460,000					12,460,000
Retained earnings (deficit)						$ (19,400,000)					(19,400,000)
Interest and other income, net*	[1]										174,000
Product [Member]
Products revenue										158,638,000	142,535,000		132,660,000
Sales and marketing											58,420,000
Product [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Products revenue											274,000
Sales and marketing											540,000
Product [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Products revenue											142,261,000
Sales and marketing											58,960,000
Service [Member]
Products revenue										$ 23,074,000	20,185,000		$ 18,833,000
Service [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Products revenue											280,000
Service [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Products revenue											$ 19,905,000

[1] Included in interest and other income, net, is the estimated interest expense for advance payment related to service contracts under the new revenue standard.