Business Segments and Geographic Information - Income Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Pre-Tax Income Reconciliation of Segments
Operating income from segments	$ 74,777	$ 64,450
Unallocated Amount:
General and Administrative Expenses	(46,424)	(41,832)
Income before income taxes and equity in earnings of affiliates	42,893	37,680
Operating Segments
Pre-Tax Income Reconciliation of Segments
Operating income from segments	121,201	106,282
Segment Reconciling Items
Unallocated Amount:
General and Administrative Expenses	(46,424)	(41,832)
Net Interest Expense	$ (31,884)	$ (26,770)