Quarterly report pursuant to Section 13 or 15(d)

Note 6 - Fair Value Measurements and Financial Instruments - Assets Measured on a Recurring Basis (Details)

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Note 6 - Fair Value Measurements and Financial Instruments - Assets Measured on a Recurring Basis (Details) - Fair Value, Recurring [Member] - USD ($)
$ in Thousands
Mar. 31, 2020
Dec. 31, 2019
Assets, fair value $ 64,836 $ 95,960
Fair Value, Inputs, Level 1 [Member]    
Assets, fair value 64,836 95,960
Bank Time Deposits [Member]    
Assets, fair value 1,321 2,989
Bank Time Deposits [Member] | Fair Value, Inputs, Level 1 [Member]    
Assets, fair value 1,321 2,989
Corporate Debt Securities [Member]    
Assets, fair value 18,873 6,235
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]    
Assets, fair value 18,873 6,235
Canadian Provincial Promissory Notes [Member]    
Assets, fair value 35,230 5,493
Canadian Provincial Promissory Notes [Member] | Fair Value, Inputs, Level 1 [Member]    
Assets, fair value 35,230 5,493
Investments [Member]    
Assets, fair value 9,412 81,243
Investments [Member] | Fair Value, Inputs, Level 1 [Member]    
Assets, fair value $ 9,412 $ 81,243