Note 4 - Accounting for Stock-based Compensation (Details Textual) - USD ($) | 3 Months Ended |
Jun. 30, 2020 | Jun. 30, 2019 |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares) | 0 | |
2006 Employee Equity Compensation Restricted Stock Plan (the "Employee Plan") [Member] | Restricted Stock [Member] | | |
Stock Issued During Period, Shares, Restricted Stock Award, Gross (in shares) | 972,175 | |
2016 Employee Equity Compensation Restricted Stock Plan [Member] | Restricted Stock [Member] | | |
Stock Issued During Period, Shares, Restricted Stock Award, Gross (in shares) | 153,608 | |
2006 Outside Director Equity Compensation Restricted Stock Plan (the "Director Plan") [Member] | Restricted Stock [Member] | | |
Stock Issued During Period, Shares, Restricted Stock Award, Gross (in shares) | 272,000 | |
2015 Outside Director Equity Compensation Restricted Stock Plan ("2015 Director Plan") [Member] | Restricted Stock [Member] | | |
Stock Issued During Period, Shares, Restricted Stock Award, Gross (in shares) | 135,000 | |
Employee and Director Plans [Member] | | |
Share-based Payment Arrangement, Expense | $ 740,000 | $ 635,000 |
Employee and Director Plans [Member] | Restricted Stock [Member] | | |
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total | $ 1,900,000 | $ 3,200,000 |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number, Ending Balance (in shares) | 183,000 | 150,000 |
Employee and Director Plans [Member] | Restricted Stock [Member] | Minimum [Member] | | |
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year) | 1 year | |
Employee and Director Plans [Member] | Restricted Stock [Member] | Maximum [Member] | | |
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year) | 3 years | |