Intangible Assets Goodwill additional (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Apr. 24, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	$ 359,688	$ 8,007	$ 345,269	$ 342,111
Goodwill, Period Increase	$ 14,419