Business Segments and Geographic Information - Income Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Pre-Tax Income Reconciliation of Segments
Total operating income from segments	$ 64,450	$ 64,372
Unallocated Amount:
General and Administrative Expenses	(41,832)	(42,586)
Income before income taxes and equity in earnings of affiliates	37,680	41,349
Operating Segments
Pre-Tax Income Reconciliation of Segments
Total operating income from segments	106,282	106,958
Segment Reconciling Items
Unallocated Amount:
General and Administrative Expenses	(41,832)	(42,586)
Net Interest Expense	$ (26,770)	$ (23,023)