Note 4 - Revisions in Estimates (Details Textual) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Gross Profit, Total	$ 51,224	$ 122,558	$ 46,758	$ 1,138	$ 30,491	$ 160,661	$ 99,424	$ 44,264	$ 221,678	$ 334,840	$ 278,741
Minimum [Member]
Gross Profit, Total										(6,400)	(6,100)
Maximum [Member]
Gross Profit, Total									(52,600)		(25,900)
Water [Member]
Gross Profit, Total									29,766	59,134	11,544
Specialty [Member]
Gross Profit, Total									86,729	89,935	92,247
Estimated Cost Recovery of Customer Affirmative Claims and Back Charges [Member] | Noncontrolling Interest [Member]
Gross Profit, Total									(9,800)	0	(2,100)
Estimated Cost Recovery of Customer Affirmative Claims and Back Charges [Member] | Minimum [Member]
Gross Profit, Total									(5,500)
Estimated Cost Recovery of Customer Affirmative Claims and Back Charges [Member] | Maximum [Member]
Gross Profit, Total										$ (49,600)
Estimated Cost Recovery of Customer Affirmative Claims and Back Charges [Member] | Water [Member]
Gross Profit, Total									(22,500)
Estimated Cost Recovery of Customer Affirmative Claims and Back Charges [Member] | Water [Member] | Minimum [Member]
Gross Profit, Total									(7,100)
Estimated Cost Recovery of Customer Affirmative Claims and Back Charges [Member] | Water [Member] | Maximum [Member]
Gross Profit, Total									(7,900)
Estimated Cost Recovery of Customer Affirmative Claims and Back Charges [Member] | Specialty [Member]
Gross Profit, Total									$ 9,000		$ 6,100