Acquisitions (Schedule of Selected Financial Information) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2015
Alkali Business [Member]
Business Acquisition [Line Items]
Revenues	$ 277,011
Net income	$ 42,014
Enterprise Offshore Acquisition [Member]
Business Acquisition [Line Items]
Revenues		$ 101,444
Net income		$ 58,805