Other Assets Other Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Other Current Assets [Line Items]
Goodwill	$ 314,143	$ 314,143	$ 331,884
Investments	44,400	41,287
Other Prepaid Expense, Current	30,099	17,937
Derivative Asset	11,909	17,482
Property, Plant and Equipment, Net	5,990	6,127
Deferred Costs and Other Assets	6,310	6,851
Parent Company [Member]
Other Current Assets [Line Items]
Other Assets	$ 412,851	$ 403,827