Note 12 - Income Taxes (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Undistributed Earnings of Foreign Subsidiaries	$ 27,700	$ 32,900
Percent of Dividend Received Deduction	100.00%
Unrecognized Tax Benefits, Ending Balance	$ 33,499	25,407	$ 20,491	$ 16,272
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	24,300	17,300
Unrecognized Tax Benefits, Interest on Income Taxes Accrued	2,400	1,600
Domestic Tax Authority [Member]
Operating Loss Carryforwards, Total	0
Domestic Tax Authority [Member] | Research Tax Credit Carryforward [Member]
Tax Credit Carryforward, Amount	7,100
State and Local Jurisdiction [Member] | Research Tax Credit Carryforward [Member]
Tax Credit Carryforward, Amount	30,500
State and Local Jurisdiction [Member] | Internal Revenue Service (IRS) [Member]
Operating Loss Carryforwards, Total	20,200
Bermuda Subsidiary [Member]
Foreign Earnings Repatriated	$ 30,000	$ 75,000