Business Segments and Geographic Information (Pre-Tax Income Reconciliation of Segments) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pre-Tax Income Reconciliation of Segments
Total operating income from segments	$ 438,628	$ 414,293	$ 372,769
Unallocated amounts:
General and administrative expense	(190,343)	(148,709)	(137,040)
Net interest expense	(96,348)	(100,222)	(94,558)
Loss on extinguishment of debt	0	(15,885)	0
Income Before Income Taxes and Equity in Earnings of Affiliates	151,937	149,477	141,171
Operating Segments
Pre-Tax Income Reconciliation of Segments
Total operating income from segments	$ 438,628	$ 414,293	$ 372,769