Note 10 - Segment Information, Significant Customers, Industry Concentration and Geographic Areas (Tables)

12 Months Ended

Dec. 31, 2019

Notes Tables

Reconciliation of Revenue from Segments to Consolidated [Table Text Block]

	Year Ended December 31,
	2019					2018					2017
	(in thousands)
	Amount		Percent			Amount		Percent			Amount		Percent
United States - domestic shipments	$	326,559		63.5		$	302,754		56.8		$	255,197		58.3
Shipments to or from Mexico		186,391		36.3			229,350		43.0			181,099		41.4
Shipments to or from Canada		1,226		0.2			1,157		0.2			1,542		0.3
Total Operating Revenues	$	514,177		100	%	$	533,261		100	%	$	437,838		100	%