Note 6 - Accrued Retirement Benefits - Fair Values of Pension Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Fair value of pension plan assets	$ 13,783	$ 32,103	$ 43,587
Fair Value, Inputs, Level 1 [Member]
Fair value of pension plan assets	0	0
Fair Value, Inputs, Level 2 [Member]
Fair value of pension plan assets	12,694	28,932
Fair Value, Inputs, Level 3 [Member]
Fair value of pension plan assets	1,089	3,171
Equity Funds [Member]
Fair value of pension plan assets	1,459	7,810
Equity Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of pension plan assets	0	0
Equity Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value of pension plan assets	631	6,385
Equity Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value of pension plan assets	828	1,425
Fixed Income Funds [Member]
Fair value of pension plan assets	10,927	22,860
Fixed Income Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of pension plan assets	0	0
Fixed Income Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value of pension plan assets	10,666	21,114
Fixed Income Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value of pension plan assets	261	1,746
Money Market Funds [Member]
Fair value of pension plan assets	1,397	1,433
Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of pension plan assets	0	0
Money Market Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value of pension plan assets	1,397	1,433
Money Market Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value of pension plan assets	$ 0	$ 0