Acquisitions (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($) item
Acquisitions
Number of acquisitions | item				0
Goodwill on acquisition		$ 143,874	$ 140,341	$ 114,588
Dyna Ten
Acquisitions
Goodwill on acquisition	$ 19,800
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets
Total purchase price	$ 40,500
Other Acquisitions
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets
Total purchase price		$ 8,300	$ 15,400