Other Assets Other Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Dec. 31, 2016
Other Current Assets [Line Items]
Goodwill	$ 320,639	$ 331,884	$ 0
Investments	42,672	41,636
Other Prepaid Expense, Current	25,771	30,332
Derivative Asset	25,472	14,515
Furniture and Fixtures, Gross	7,010	6,123
Deferred Costs and Other Assets	7,933	2,637
Parent Company [Member]
Other Current Assets [Line Items]
Other Assets	$ 429,497	$ 427,127