Acquisitions (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($) item	Mar. 31, 2015 USD ($) item	Sep. 30, 2015 USD ($) item	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Acquisitions
Goodwill on acquisition	$ 143,674		$ 143,674		$ 140,341	$ 114,588
Dyna Ten
Acquisitions
Total purchase price		$ 40,500
Goodwill on acquisition		$ 19,800
Other Acquisitions
Acquisitions
Total purchase price			$ 7,100	$ 9,500
Number of acquisitions | item	1	2	3