Revenues (Customer Liability) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Revenue from Contract with Customer [Abstract]
Contract liability	$ 10,094		$ 7,786
Contract with Customer, Liability, Revenue Recognized	$ 3,700	$ 3,000