Note 2 - Summary of Significant Accounting Policies - Valuation Assumptions (Details)		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Dividend yield	[1]	0.00%	0.00%
Expected volatility	[2]	28.81%	28.22%
Expected life (Year)	[3]	6 years 91 days	6 years 91 days
Assumed forfeiture rate	[4]	4.00%	4.00%
Minimum [Member]
Risk-free interest rate	[5]	2.47%	2.38%
Expected life (Year)	[3]		7 years
Maximum [Member]
Risk-free interest rate	[5]	2.70%	2.84%

[1] A dividend yield of 0.0% is utilized because cash dividends have never been paid.

[2] The expected volatility was based on the historical volatility of the Company's common stock price as adjusted for certain historical periods of extraordinary volatility in order to provide a basis for a reasonable estimate of fair value.

[3] The expected life reflects a 1 to 4 year vesting period, the maximum ten year term and review of historical behavior.

[4] Forfeiture rate is determined through forfeited and expired options as a percentage of options granted over the current three year period.

[5] The risk-free interest rate is based on the five to seven year Treasury bond.