Note 7 - Accrued Retirement Benefits - Fair Values of Pension Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Fair value of pension plan assets	$ 13,860	$ 13,783	$ 32,103
Equity Funds [Member]
Fair value of pension plan assets	760	1,459
Fixed Income Funds [Member]
Fair value of pension plan assets	12,072	10,927
Money Market Funds [Member]
Fair value of pension plan assets	1,028	1,397
Fair Value, Inputs, Level 1 [Member]
Fair value of pension plan assets	0	0
Fair Value, Inputs, Level 1 [Member] | Equity Funds [Member]
Fair value of pension plan assets	0	0
Fair Value, Inputs, Level 1 [Member] | Fixed Income Funds [Member]
Fair value of pension plan assets	0	0
Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Fair value of pension plan assets	0	0
Fair Value, Inputs, Level 2 [Member]
Fair value of pension plan assets	13,790	12,694
Fair Value, Inputs, Level 2 [Member] | Equity Funds [Member]
Fair value of pension plan assets	760	631
Fair Value, Inputs, Level 2 [Member] | Fixed Income Funds [Member]
Fair value of pension plan assets	12,002	10,666
Fair Value, Inputs, Level 2 [Member] | Money Market Funds [Member]
Fair value of pension plan assets	1,028	1,397
Fair Value, Inputs, Level 3 [Member]
Fair value of pension plan assets	70	1,089
Fair Value, Inputs, Level 3 [Member] | Equity Funds [Member]
Fair value of pension plan assets	0	828
Fair Value, Inputs, Level 3 [Member] | Fixed Income Funds [Member]
Fair value of pension plan assets	70	261
Fair Value, Inputs, Level 3 [Member] | Money Market Funds [Member]
Fair value of pension plan assets	$ 0	$ 0