Note 9 - Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2019

Notes Tables

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

	2019			2018			2017
Dividend yield		0.96	%		1.20	%		0.70	%
Volatility		42.8	%		41.3	%		39.1	%
Risk-free interest rate		1.7	%		2.7	%		2.2	%
Weighted average expected option term (in years)		4.7			4.8			4.6
Weighted average fair value per share of options granted	$	12.51		$	8.28		$	10.37

Share-based Payment Arrangement, Option, Activity [Table Text Block]

				Weighted		Weighted Average	Aggregate
	Number			Average		Remaining	Intrinsic
	of Shares			Exercise Price		Contractual Term	Value
						(in years)
Balance outstanding at December 31, 2018 (1)		1,462,575		$	16.41	4.54	$	12,214,422
Granted		195,379		$	35.53
Exercised (2)		(509,693	)	$	9.53		$	11,488,292
Canceled / Expired		(101,167	)	$	17.90
Balance outstanding at December 31, 2019 (3)		1,047,094		$	23.19	4.31	$	13,366,595
Vested and exercisable at December 31, 2019 (4)		309,501		$	19.64	3.50	$	5,046,733
Expected to vest at December 31, 2019		737,593		$	24.68	4.65
Total		1,047,094

Share-based Payment Arrangement, Restricted Stock Unit, Activity [Table Text Block]

				Weighted
				Average
				Grant Date
	Shares			Fair Value
Balance outstanding at December 31, 2018		217,895		$	21.21
Granted		56,567		$	35.41
Vested (1)		(61,058	)	$	18.46
Canceled		(24,723	)	$	22.19
Balance outstanding at December 31, 2019		188,681		$	26.14

Accelerated Share Repurchases [Table Text Block]

	2019		2018
Shares of common stock repurchased		20,524		21,410
Average per share repurchase price	$	33.28	$	34.62
Aggregage purchase price (in thousands)	$	683	$	741

Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block]

	2019		2018		2017
	(in thousands)
Stock option awards	$	1,580	$	1,457	$	1,612
Restricted stock units		1,062		892		644
Total stock-based compensation	$	2,642	$	2,349	$	2,256

	2019		2018		2017
	(in thousands)
Cost of sales	$	310	$	272	$	188
Sales and marketing		544		529		403
General and administrative		1,509		1,293		1,484
Research and development		279		255		181
Total stock-based compensation	$	2,642	$	2,349	$	2,256

Schedule of Dividends Payable [Table Text Block]

Record Date	Payment Date	Per Share Amount		Dividend Payment
				(in thousands)
Fiscal Year 2019
March 22, 2019	April 5, 2019	$	0.085	$	1,672
May 22, 2019	June 6, 2019	$	0.085	$	1,672
August 21, 2019	September 5, 2019	$	0.085	$	1,691
November 20, 2019	December 5, 2019	$	0.085	$	1,701
Fiscal Year 2018
March 22, 2018	April 5, 2018	$	0.070	$	1,351
May 22, 2018	June 7, 2018	$	0.070	$	1,353
August 22, 2018	September 6, 2018	$	0.070	$	1,369
November 20, 2018	December 6, 2018	$	0.070	$	1,372