Note 6 - Share-based Payments - Summary of Status of Employees' Restricted Stock Awards (Details) - Employees [Member] - Restricted Stock [Member] - USD ($)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Nonvested, Beginning of Year (in shares)	2,895	7,180	13,581
Nonvested, Beginning of Year, weighted average grant-date fair value (in dollars per share)	$ 29.41	$ 29.72	$ 28.56
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value
Vested (in shares)	2,895	4,285	6,401
Vested, weighted average grant-date fair value (in dollars per share)	$ 29.41	$ 29.94	$ 27.25
Forfeited (in shares)
Forfeited, weighted average grant-date fair value (in dollars per share)
Nonvested, End of Year (in shares)		2,895	7,180
Nonvested, End of Year, weighted average grant-date fair value (in dollars per share)		$ 29.41	$ 29.72
Allocated Share-based Compensation Expense, Total	$ 16,000	$ 70,000	$ 96,000
Fair Value of Awards Vested	$ 85,000	$ 128,000	$ 174,000

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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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 weighted average fair value at grant date for nonvested equity-based awards issued 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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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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