Note 9 - Employee Retirement Plans - Pension Plan Measured at Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Fair value of plan assets	$ 56,495	$ 59,625	$ 56,790	$ 57,536
Pension Plan [Member]
Total		59,095
Accrued income		530
Pension Plan [Member] \| Change In Plan Assets [Member]
Fair value of plan assets	56,495	59,625
Pension Plan [Member] \| Fair Value, Inputs, Level 1 [Member]
Total		6,569
Accrued income		530
Pension Plan [Member] \| Fair Value, Inputs, Level 1 [Member] \| Change In Plan Assets [Member]
Fair value of plan assets	39,705	7,099
Pension Plan [Member] \| Fair Value, Inputs, Level 2 [Member]
Total		52,526
Accrued income		0
Pension Plan [Member] \| Fair Value, Inputs, Level 2 [Member] \| Change In Plan Assets [Member]
Fair value of plan assets	1,626	52,526
Pension Plan [Member] \| Fair Value, Inputs, Level 3 [Member]
Total		0
Accrued income		0
Pension Plan [Member] \| Fair Value, Inputs, Level 3 [Member] \| Change In Plan Assets [Member]
Fair value of plan assets	0	0
Pension Plan [Member] \| Fair Value Measured at Net Asset Value Per Share [Member] \| Change In Plan Assets [Member]
Fair value of plan assets	15,164
Pension Plan [Member] \| Defined Benefit Plan, Equity Securities [Member]
Fair value of plan assets	24,947	699
Pension Plan [Member] \| Defined Benefit Plan, Equity Securities [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets	21,780	699
Pension Plan [Member] \| Defined Benefit Plan, Equity Securities [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets	0	0
Pension Plan [Member] \| Defined Benefit Plan, Equity Securities [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets	0	0
Pension Plan [Member] \| Defined Benefit Plan, Equity Securities [Member] \| Fair Value Measured at Net Asset Value Per Share [Member]
Fair value of plan assets	3,167	0
Total		0
Accrued income		0
Pension Plan [Member] \| Defined Benefit Plan, Debt Security [Member]
Fair value of plan assets	29,922
Pension Plan [Member] \| Defined Benefit Plan, Debt Security [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets	17,925
Pension Plan [Member] \| Defined Benefit Plan, Debt Security [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets	0
Pension Plan [Member] \| Defined Benefit Plan, Debt Security [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets	0
Pension Plan [Member] \| Defined Benefit Plan, Debt Security [Member] \| Fair Value Measured at Net Asset Value Per Share [Member]
Fair value of plan assets	11,997
Pension Plan [Member] \| US Government Agencies Debt Securities [Member]
Fair value of plan assets		5,870
Pension Plan [Member] \| US Government Agencies Debt Securities [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets		5,870
Pension Plan [Member] \| US Government Agencies Debt Securities [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets		0
Pension Plan [Member] \| US Government Agencies Debt Securities [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets		0
Pension Plan [Member] \| Defined Benefit Plan, Cash and Cash Equivalents [Member]
Fair value of plan assets	1,626	2,526
Pension Plan [Member] \| Defined Benefit Plan, Cash and Cash Equivalents [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets	0	0
Pension Plan [Member] \| Defined Benefit Plan, Cash and Cash Equivalents [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets	1,626	2,526
Pension Plan [Member] \| Defined Benefit Plan, Cash and Cash Equivalents [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets	0	0
Pension Plan [Member] \| Defined Benefit Plan, Cash and Cash Equivalents [Member] \| Fair Value Measured at Net Asset Value Per Share [Member]
Fair value of plan assets	$ 0
Pension Plan [Member] \| Collateralized Mortgage Backed Securities [Member]
Fair value of plan assets		765
Pension Plan [Member] \| Collateralized Mortgage Backed Securities [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets		0
Pension Plan [Member] \| Collateralized Mortgage Backed Securities [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets		765
Pension Plan [Member] \| Collateralized Mortgage Backed Securities [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets		0
Pension Plan [Member] \| Corporate Debt Securities [Member]
Fair value of plan assets		47,839
Pension Plan [Member] \| Corporate Debt Securities [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets		0
Pension Plan [Member] \| Corporate Debt Securities [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets		47,839
Pension Plan [Member] \| Corporate Debt Securities [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets		0
Pension Plan [Member] \| Defined Benefit Plan Other Asset [Member]
Fair value of plan assets		1,396
Pension Plan [Member] \| Defined Benefit Plan Other Asset [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets		0
Pension Plan [Member] \| Defined Benefit Plan Other Asset [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets		1,396
Pension Plan [Member] \| Defined Benefit Plan Other Asset [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets		$ 0