Note 2 - Revenue Recognition - Summary of Effects of Adopting Topic 606 on the Condensed Consolidated Financial Statements (Details) - USD ($)		3 Months Ended			9 Months Ended
		Sep. 30, 2018		Sep. 30, 2017	Sep. 30, 2018		Sep. 30, 2017	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Other long-term assets		$ 6,048,000			$ 6,048,000					$ 374,000
Deferred tax asset		21,402,000			21,402,000					19,055,000
Accrued liabilities		22,904,000			22,904,000					26,848,000
Deferred revenue		11,319,000		$ 9,958,000	11,319,000		$ 9,958,000	$ 11,807,000		11,656,000	$ 10,013,000	$ 9,431,000
Retained earnings (deficit)		2,283,000			2,283,000					$ 2,947,000
Products revenue		40,573,000		38,173,000	117,251,000		103,861,000
Sales and marketing		14,479,000		13,148,000	43,102,000		36,708,000
Interest and other income, net*		(49,000)	[1]	197,000	(80,000)	[1]	746,000
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		5,380,000			5,380,000
Deferred tax asset		(1,160,000)			(1,160,000)
Accrued liabilities		(111,000)			(111,000)
Deferred revenue		195,000			195,000
Retained earnings (deficit)		4,415,000			4,415,000
Interest and other income, net*	[1]	(55,000)			(184,000)
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Other long-term assets		668,000			668,000
Deferred tax asset		22,562,000			22,562,000
Accrued liabilities		23,015,000			23,015,000
Deferred revenue		11,124,000			11,124,000
Retained earnings (deficit)		(2,132,000)			(2,132,000)
Interest and other income, net*	[1]	6,000			104,000
Product [Member]
Products revenue		35,675,000		33,486,000	102,589,000		89,688,000
Sales and marketing		14,479,000			43,102,000
Product [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Products revenue		(56,000)			9,000
Sales and marketing		(55,000)			(703,000)
Product [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Products revenue		35,731,000			102,580,000
Sales and marketing		14,534,000			43,805,000
Service [Member]
Products revenue		4,898,000		$ 4,687,000	14,662,000		$ 14,173,000
Service [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Products revenue		(59,000)			74,000
Service [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Products revenue		$ 4,957,000			$ 14,588,000

[1] Included in interest and other income, net is the estimated interest expense for advance payment related to contract services under the new revenue standard going forward. Adoption of the standard had no impact to total net cash from or used in operating, investing, or financing activities within the Condensed Consolidated Statements of Cash Flows.