Note 3 - Impact of Recently Issued Accounting Pronouncements (Details Textual) - USD ($) $ in Thousands		3 Months Ended	12 Months Ended
	Jan. 01, 2018	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Retained earnings			$ 538,463	$ 429,826
Gross sales			514,997	525,936	$ 491,538
Cost of goods sold			335,405	304,153	286,256
Tax Expense			16,596	38,061	40,214
Income tax expense benefit measurement period adjustment		$ (2,105)	2,105
Accounting Standards Updated 2014-09 [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Retained earnings	$ 16,219		5,119
Gross sales	51,896		(19,781)
Cost of goods sold	31,347		(5,753)
Tax Expense	$ 4,330		(2,928)
Accounting Standards Update 2017-07 [Member] | Other Expenses, Net [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Defined benefit plan, other costs			$ 813
Accounting Standards Update 2017-07 [Member] | Restatement Adjustment [Member] | Selling, General and Administrative Expenses [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Defined benefit plan, other costs				1,484	1,540
Accounting Standards Update 2017-07 [Member] | Restatement Adjustment [Member] | Cost of Goods Sold [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Defined benefit plan, other costs				$ 216	$ 163