Note 2 - Impact of Recently Issued Accounting Pronouncements (Details Textual) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
	Jan. 01, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Retained earnings		$ 537,251		$ 537,251		$ 429,826
Gross sales		104,231	$ 112,233	390,575	$ 350,431
Cost of goods sold		71,893	65,676	249,389	200,802
Tax Expense		(15,406)	7,498	(872)	22,484
Income tax expense benefit measurement period adjustment				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	36,131		36,131
Gross sales	51,896	1,914		58,182
Cost of goods sold	31,347	8,475		33,194
Tax Expense	$ 4,330	(1,558)		5,076
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		$ 167		$ 649
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			(384)		(1,107)
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			$ (54)		$ (161)