Note 15 - Employee Benefit Plans - Fair Values of Pension Plan Assets, by Asset Category (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Plan assets at fair value	$ 9,157	$ 8,092	$ 8,513
Fair Value, Inputs, Level 1 [Member]
Plan assets at fair value	9,157	8,092
Fair Value, Inputs, Level 2 [Member]
Plan assets at fair value
Fair Value, Inputs, Level 3 [Member]
Plan assets at fair value
Defined Benefit Plan, Cash Equivalents and Short-term Investments [Member]
Plan assets at fair value
Defined Benefit Plan, Cash Equivalents and Short-term Investments [Member] | Fair Value, Inputs, Level 1 [Member]
Plan assets at fair value
Defined Benefit Plan, Cash Equivalents and Short-term Investments [Member] | Fair Value, Inputs, Level 2 [Member]
Plan assets at fair value
Defined Benefit Plan, Cash Equivalents and Short-term Investments [Member] | Fair Value, Inputs, Level 3 [Member]
Plan assets at fair value
Mutual Fund [Member] | Equity Securities [Member]
Plan assets at fair value	4,749	3,848
Mutual Fund [Member] | Fixed Income Securities [Member]
Plan assets at fair value	4,408
Mutual Fund [Member] | Fair Value, Inputs, Level 1 [Member] | Equity Securities [Member]
Plan assets at fair value	4,749	3,848
Mutual Fund [Member] | Fair Value, Inputs, Level 1 [Member] | Fixed Income Securities [Member]
Plan assets at fair value	4,408
Mutual Fund [Member] | Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member]
Plan assets at fair value
Mutual Fund [Member] | Fair Value, Inputs, Level 2 [Member] | Fixed Income Securities [Member]
Plan assets at fair value
Mutual Fund [Member] | Fair Value, Inputs, Level 3 [Member] | Equity Securities [Member]
Plan assets at fair value
Mutual Fund [Member] | Fair Value, Inputs, Level 3 [Member] | Fixed Income Securities [Member]
Plan assets at fair value
Defined Benefit Plan, Cash and Cash Equivalents [Member] | Fixed Income Securities [Member]
Plan assets at fair value		4,244
Defined Benefit Plan, Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member] | Fixed Income Securities [Member]
Plan assets at fair value		4,244
Defined Benefit Plan, Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member] | Fixed Income Securities [Member]
Plan assets at fair value
Defined Benefit Plan, Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 3 [Member] | Fixed Income Securities [Member]
Plan assets at fair value