Note 4 - Accounting for Stock-based Compensation (Details Textual) - USD ($)	3 Months Ended
Jun. 30, 2021	Jun. 30, 2020
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)	1,380	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
The 2016 Employee Equity Compensation Restricted Stock Plan [Member] \| Restricted Stock [Member]
Stock Issued During Period, Shares, Restricted Stock Award, Gross (in shares)	218,180
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)	173,880
2015 Outside Director Equity Compensation Restricted Stock Plan ("2015 Director Plan") [Member] \| Restricted Stock [Member] \| Minimum [Member]
Restriction Period (Year)	1 year
2015 Outside Director Equity Compensation Restricted Stock Plan ("2015 Director Plan") [Member] \| Restricted Stock [Member] \| Maximum [Member]
Restriction Period (Year)	3 years
Employee and Director Plans [Member]
Share-based Payment Arrangement, Expense	$ 718,000	$ 740,000
Employee and Director Plans [Member] \| Restricted Stock [Member]
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total	$ 1,900,000	$ 1,900,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number, Ending Balance (in shares)	160,638	182,695
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

Period of restriction of forfeiture.

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Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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-Publisher FASB
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-Section 50
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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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Total number of shares issued during the period, including shares forfeited, as a result of Restricted Stock Awards.

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