Note 6 - Accrued Retirement Benefits - Fair Values of Pension Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair value of pension plan assets	$ 47,176	$ 56,434	$ 64,341
Fair Value, Inputs, Level 1 [Member]
Fair value of pension plan assets
Fair Value, Inputs, Level 2 [Member]
Fair value of pension plan assets	47,176	56,434
Fair Value, Inputs, Level 3 [Member]
Fair value of pension plan assets	47,176	56,434
Equity Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of pension plan assets
Equity Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value of pension plan assets	7,177	8,120
Equity Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value of pension plan assets	7,177	8,120
Fixed Income Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of pension plan assets
Fixed Income Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value of pension plan assets	39,025	46,069
Fixed Income Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value of pension plan assets	39,025	46,069
Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of pension plan assets
Money Market Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value of pension plan assets	974	2,245
Money Market Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value of pension plan assets	$ 974	$ 2,245