Quarterly report pursuant to Section 13 or 15(d)

Note 10 - Stock-based Compensation (Details Textual)

v3.19.1
Note 10 - Stock-based Compensation (Details Textual) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Maximum Subscription Rate 17.50%    
Share-based Compensation Arrangement by Share-based Payment Award, Maximum Number of Shares 7,300,000    
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period 4 years    
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period 10 years    
Share-based Payment Arrangement, Nonvested Award, Option, Cost Not yet Recognized, Amount $ 2,190    
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition 1 year 259 days    
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance 5,784,000   4,489,000
Employee Stock Option Vesting Schedule II [Member]      
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance 335,000 91,000  
Employee Stock Option Vesting Schedule III [Member]      
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance   850,000  
Share-based Payment Arrangement, Tranche One [Member]      
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage 50.00% 50.00%  
Share-based Payment Arrangement, Tranche One [Member] | Employee Stock Option Vesting Schedule II [Member]      
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage 100.00% 50.00%  
Share-based Payment Arrangement, Tranche Two [Member]      
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage 16.67% 16.67%  
Share-based Payment Arrangement, Tranche Two [Member] | Employee Stock Option Vesting Schedule II [Member]      
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage   25.00%  
Share-based Compensation Award, Tranche Four [Member]      
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage 16.67% 16.67%  
Share-based Payment Arrangement, Tranche Three [Member]      
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage 16.67% 16.67%  
Share-based Payment Arrangement, Tranche Three [Member] | Employee Stock Option Vesting Schedule II [Member]      
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage   25.00%