Basis of Condensed Consolidated Financial Statements (AOCI Table) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cumulative foreign currency translation	$ (99,755)		$ (95,630)
Cumulative supplemental benefit plans	(6,760)		(5,461)
Net unrecognized gains on interest rate swaps	13,131		7,400
Accumulated other comprehensive loss	$ (93,384)	$ (93,700)	$ (93,691)