Note 9 - Fair Value of Financial Instruments - Fair Value Measurements, Not Recorded (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Liabilities
Revolver	$ 304,484	$ 196,235
Carrying Value [Member]
Liabilities
Total liabilities not recorded at fair value	304,484	197,165
Industrial Revenue Bonds [Member]
Liabilities
IRB		930
Fair Value, Inputs, Level 1 [Member] | Carrying Value [Member]
Liabilities
Total liabilities not recorded at fair value		930
Fair Value, Inputs, Level 1 [Member] | Industrial Revenue Bonds [Member]
Liabilities
IRB		930
Fair Value, Inputs, Level 2 [Member] | Carrying Value [Member]
Liabilities
Total liabilities not recorded at fair value	304,484	196,235
Fair Value, Inputs, Level 2 [Member] | Industrial Revenue Bonds [Member]
Liabilities
IRB
Fair Value, Inputs, Level 3 [Member] | Carrying Value [Member]
Liabilities
Total liabilities not recorded at fair value
Fair Value, Inputs, Level 3 [Member] | Industrial Revenue Bonds [Member]
Liabilities
IRB
Revolver [Member]
Liabilities
Revolver	304,484	196,235
Revolver [Member] | Fair Value, Inputs, Level 1 [Member]
Liabilities
Revolver
Revolver [Member] | Fair Value, Inputs, Level 2 [Member]
Liabilities
Revolver	304,484	196,235
Revolver [Member] | Fair Value, Inputs, Level 3 [Member]
Liabilities
Revolver