Note 1 - Basis of Presentation and Accounting Policies (Details Textual) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Cost of Goods and Services Sold, Total	$ 104,537	$ 89,882	$ 190,241	$ 168,104
Selling, General and Administrative Expense, Total	21,828	19,079	43,569	39,772
Nonoperating Income (Expense), Total	113	1,195	660	(905)
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	$ 431	395	$ 864	790
Revision of Prior Period, Adjustment [Member] | Cost of Sales Reclassified to Other (Expense) Income, Net [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total				500
Cost of Goods and Services Sold, Total		500		200
Selling, General and Administrative Expense, Total		1,000
Nonoperating Income (Expense), Total		500		200
Revision of Prior Period, Adjustment [Member] | Selling, General and Administrative Expenses Reclassified to Other (Expense) Income, Net [Member]
Selling, General and Administrative Expense, Total				300
Nonoperating Income (Expense), Total		1,000		$ 300
Revision of Prior Period, Adjustment [Member] | Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total		$ (1,500)