Note 2 - Impact of Recently Issued Accounting Pronouncements (Details Textual) - USD ($) $ in Thousands		3 Months Ended
	Jan. 01, 2018	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Retained earnings		$ 470,103		$ 429,826
Gross sales		139,130	$ 103,711
Cost of goods sold		90,242	58,131
Tax Expense		5,786	5,812
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	29,629
Gross sales	51,896	37,280
Cost of goods sold	31,347	20,699
Tax Expense	$ 4,330	3,171
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		$ 311
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			(363)
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			$ (50)