Acquisitions (Narrative) (Details) - USD ($)				12 Months Ended
	Nov. 23, 2015	Mar. 13, 2015	Jan. 13, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition
Payment to acquire business, net of cash acquired				$ 0	$ 0	$ 196,001,000
Business acquisition cost				$ 0	$ 0	$ 760,000
TEW Plus LTD
Business Acquisition
Acquisition date	Nov. 23, 2015
Percentage of voting interests acquired	75.00%
Name of acquired entity	TEW Plus, Ltd (“Tew Plus”)
Payment to acquire business, net of cash acquired	$ 2,130,000
Inspection Oilfield Services (IOS)
Business Acquisition
Acquisition date		Mar. 13, 2015
Name of acquired entity		IOS Holdings, Inc. (“IOS” or ”Test and Inspection Services”)
Payment to acquire business, net of cash acquired		$ 167,404,000
Working capital adjustment		2,363,000
Earn out provision		60,000,000
Indemnified assets		$ 7,600,000
TEW Holdings, LTD
Business Acquisition
Acquisition date			Jan. 13, 2015
Name of acquired entity			TEW Holdings, Ltd (“Tew”)
Payment to acquire business, net of cash acquired			$ 26,467,000
Working capital adjustment			4,200,000
Indemnified assets			$ 600,000