Note 1 - Summary of Significant Accounting Policies (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2017		Jan. 01, 2019	Jan. 01, 2018	Dec. 31, 2016
Cumulative Effect of New Accounting Principle in Period of Adoption								$ 3,813,000
Deferred Revenue, Total		$ 12,566,000
Capitalized Contract Cost, Net, Total	$ 4,600,000	5,200,000
Operating Lease, Right-of-Use Asset	7,702,000					$ 10,049,000
Operating Lease, Liability, Total	7,912,000
Contract with Customer, Liability, Total	14,222,000	12,566,000	[1]	$ 11,656,000	[1]		$ 11,656,000
Revenue from Contract with Customer, Including Assessed Tax	181,712,000	162,720,000		151,493,000
Other-than-temporary Impairment Loss, Debt Securities, Available-for-sale, Total	0	0		0
Inventory, Finished Goods, Gross, Total	4,100,000	2,900,000
Depreciation, Total	$ 1,500,000	1,200,000		1,000,000
Number of Operating Segments	1
Goodwill, Impairment Loss	$ 0
Advertising Expense	$ 2,800,000	2,800,000		1,800,000
Minimum [Member] | Distributors [Member]
Standard Warranty Period	1 year 60 days
Maximum [Member] | Distributors [Member]
Standard Warranty Period	1 year 120 days
Capitalized Cloud Computing Set-up Cost [Member] | Minimum [Member]
Finite-Lived Intangible Asset, Useful Life	3 years
Capitalized Cloud Computing Set-up Cost [Member] | Maximum [Member]
Finite-Lived Intangible Asset, Useful Life	5 years
UNITED STATES
Revenue from Contract with Customer, Including Assessed Tax	$ 106,243,000	$ 101,862,000		$ 94,581,000
Percentage of Assets	89.30%	89.00%
Customer Concentration Risk [Member] | Revenue Benchmark [Member] | UNITED STATES
Concentration Risk, Percentage	58.00%	62.00%		62.00%
Customer Concentration Risk [Member] | Revenue Benchmark [Member] | Non-US [Member]
Concentration Risk, Percentage	42.00%	38.00%		38.00%
Selling and Marketing Expense [Member]
Capitalized Contract Cost, Amortization	$ 2,900,000	$ 1,800,000
Loyalty [Member]
Contract with Customer, Liability, Total	200,000
Service [Member]
Revenue from Contract with Customer, Including Assessed Tax	$ 23,074,000	$ 20,185,000		$ 18,833,000
Bill and Hold Arrangement [Member]
Revenue from Contract with Customer, Including Assessed Tax				$ 938,000
Transferred over Time [Member]
Revenue from Contract with Customer, Including Assessed Tax, Percent of Total Revenues	13.00%	12.00%
Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption								$ 3,813,000
Accounting Standards Update 2014-09 [Member]
Deferred Revenue, Total							(237,000)
Extended Product Warranty Accrual, Ending Balance							151,000
Variable Consideration							210,000
Capitalized Contract Cost, Net, Total							4,700,000
Deferred Income Tax Liabilities, Net, Total							1,200,000
Accounting Standards Update 2014-09 [Member] | Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption							$ 3,800,000
Accounting Standards Update 2016-02 [Member]
Operating Lease, Right-of-Use Asset						10,200,000
Operating Lease, Liability, Total						$ 10,100,000

[1] The 2018 presentation in the table above has been revised to include deferred revenue of $11,656 at January 1, 2018 and $12,566 at December 31, 2018 and related changes therein that were previously excluded.