Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accrued Liabilities [Abstract]
Interest	$ 30,018	$ 30,262
Employee related costs	100,729	117,850
Income taxes payable	1,527	19,558
Other accrued expenses	132,644	95,406
Total accrued liabilities	$ 264,918	$ 263,076