Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accrued Liabilities [Abstract]
Interest	$ 30,262	$ 15,770
Employee related costs	117,850	122,590
Income taxes payable	19,558	43,083
Other accrued expenses	95,406	102,986
Total accrued liabilities	$ 263,076	$ 284,429