Note 8 - Employee Benefit Plans - Fair Value Measurements (Details) - USD ($) $ in Thousands		Dec. 31, 2019	Dec. 31, 2018
Fair value, plan assets		$ 25,007	$ 21,786
Fair Value, Inputs, Level 1 [Member]
Fair value, plan assets		19,125	13,344
Fair Value, Inputs, Level 2 [Member]
Fair value, plan assets		5,882	8,442
Fair Value, Inputs, Level 3 [Member]
Fair value, plan assets		0	0
Cash [Member]
Fair value, plan assets		4,350	1,917
Cash [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value, plan assets		4,350	1,917
Cash [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value, plan assets		0	0
Cash [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value, plan assets		0	0
Defined Benefit Plan, Equity Securities, US [Member]
Fair value, plan assets		11,098	8,782
Defined Benefit Plan, Equity Securities, US [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value, plan assets		11,098	8,782
Defined Benefit Plan, Equity Securities, US [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value, plan assets		0	0
Defined Benefit Plan, Equity Securities, US [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value, plan assets		0	0
Defined Benefit Plan, Equity Securities, Non-US [Member]
Fair value, plan assets		2,334	471
Defined Benefit Plan, Equity Securities, Non-US [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value, plan assets		2,334	471
Defined Benefit Plan, Equity Securities, Non-US [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value, plan assets		0	0
Defined Benefit Plan, Equity Securities, Non-US [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value, plan assets		0	0
Equity Funds [Member]
Fair value, plan assets	[1]	1,343	2,174
Equity Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value, plan assets	[1]	1,343	2,174
Equity Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value, plan assets	[1]	0	0
Equity Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value, plan assets	[1]	0	0
US States and Political Subdivisions Debt Securities [Member]
Fair value, plan assets		202	202
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value, plan assets		0	0
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value, plan assets		202	202
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value, plan assets		0	0
US Government Corporations and Agencies Securities [Member]
Fair value, plan assets			50
US Government Corporations and Agencies Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value, plan assets			0
US Government Corporations and Agencies Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value, plan assets			50
US Government Corporations and Agencies Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value, plan assets			0
Corporate Debt Securities [Member]
Fair value, plan assets	[2]	5,680	8,190
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value, plan assets	[2]	0	0
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value, plan assets	[2]	5,680	8,190
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value, plan assets	[2]	$ 0	$ 0

[1] This category comprises actively managed equity funds invested in large-cap and mid-cap U.S. companies.

[2] This category represents investment grade bonds of U.S. issuers from diverse industries.