Note 8 - Debt (Details Textual) $ in Thousands			12 Months Ended
	Nov. 30, 2018 USD ($)	Mar. 01, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jul. 31, 2011 USD ($)
Prepaid Expense and Other Assets, Current			$ 9,460	$ 8,333
Interest Paid, Including Capitalized Interest, Operating and Investing Activities, Total			10,200	6,400	$ 4,300
Long-term Debt, Gross			$ 275,300	$ 200,600	$ 152,500
Industrial Revenue Bonds [Member]
Repayments of Long-term Debt, Total		$ 900
All Debt, Excluding Deferred Financing Fees and Deferred Commitment Fees [Member]
Debt Instrument, Interest Rate, Effective Percentage			3.70%	3.00%	2.40%
Chicago Tube and Iron Company Acquisition [Member] | Industrial Revenue Bonds [Member]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt						$ 5,900
Amortized Banking Fees [Member]
Prepaid Expense and Other Assets, Current			$ 1,600
ABL Credit Facility [Member]
Debt Instrument, Term			5 years
Asset Based Revolving Credit Facility Due December 8, 2022 [Member] | ABL Credit Facility [Member]
Line of Credit Facility, Increase (Decrease), Net, Total	$ 75,000
Line of Credit Facility, Maximum Borrowing Capacity	445,000
Letters of Credit, Maximum Borrowing Capacity	20,000
Maximum First In, Last Out Revolving Credit Facility	30,000
Line of Credit Facility, Additional Commitments, Maximum	200,000
Line Of Credit Facility Covenant Terms Monetary	$ 30,000
Line of Credit Facility Covenant Terms Percentage of Revolver Commitments	10.00%
Balance Required for Compliance with Revolver Commitments			$ 47,500
Line of Credit Facility Covenant Terms Percentage of Aggregate Borrowing Base	10.00%
Line of Credit Facility Covenant Terms Aggregate Borrowing Base			44,400
Line of Credit Facility Covenant Terms EBITDA Ratio	1
Line of Credit Facility, Remaining Borrowing Capacity			$ 139,300
Asset Based Revolving Credit Facility Due December 8, 2022 [Member] | ABL Credit Facility [Member] | Base Rate [Member] | Minimum [Member]
Debt Instrument, Basis Spread on Variable Rate	0.00%
Asset Based Revolving Credit Facility Due December 8, 2022 [Member] | ABL Credit Facility [Member] | Base Rate [Member] | Maximum [Member]
Debt Instrument, Basis Spread on Variable Rate	0.25%
Asset Based Revolving Credit Facility Due December 8, 2022 [Member] | ABL Credit Facility [Member] | London Interbank Offered Rate (LIBOR) [Member] | Minimum [Member]
Debt Instrument, Basis Spread on Variable Rate	1.25%
Asset Based Revolving Credit Facility Due December 8, 2022 [Member] | ABL Credit Facility [Member] | London Interbank Offered Rate (LIBOR) [Member] | Maximum [Member]
Debt Instrument, Basis Spread on Variable Rate	2.75%