Note 10 - Shareholders' Equity (Details Textual) - USD ($) xbrli-pure in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Stock Repurchased and Retired During Period, Shares (in shares)	223,100	683,910
Payments for Repurchase of Common Stock	$ 2,666,000	$ 2,548,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 4,486,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)	370,000
Share-based Payment Arrangement, Expense	$ 375,000	$ 451,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total	$ 227,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)	1 year 58 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance (in shares)	568,740	1,326,414	1,022,913
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate		0.00%
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value	$ 10,772,000	$ 121,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period (in shares)	757,674	66,499
Proceeds from Stock Options Exercised	$ 1,998,000
Share-based Payment Arrangement, Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount (in shares)		455,000
The2004 Plan Member
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in shares)	5,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)	5,009,750
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year)	3 years
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period (Year)	5 years
Incentive Plan 2020 [Member]
Common Stock, Capital Shares Reserved for Future Issuance (in shares)	1,800,000
Incentive Plan 2020 [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year)	1 year
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)	8,912
Share-based Payment Arrangement, Expense	$ 6,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total	$ 102,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)	343 days