Note 7 - Income Taxes - Income Tax Reconciliation (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Expected federal income taxes	$ 11,999,000	$ 10,975,000	$ 9,576,000
Foreign tax rate differential	(131,000)	(129,000)	(139,000)
State income taxes, net of federal benefit and state tax credits	608,000	436,000	391,000
Federal tax credits	(130,000)	(165,000)	(150,000)
Uncertain tax positions	151,000	6,000	93,000
Nondeductible expenses related to proposed recapitalization	504,000
Share based compensation	(1,564,000)	(441,000)
Compensation limit for covered employees	955,000
Impact of 2017 Tax Act	(2,415,000)
Valuation allowance	535,000
Withholding tax on repatriation of foreign earnings	706,000
Other	122,000	156,000	(21,000)
Total	$ 11,340,000	$ 10,838,000	$ 9,750,000