Commitments and Contingencies (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Commitments And Contingencies [Line Items]
Rent expense under operating leases	$ 143,513	$ 145,176	$ 125,103
Standby letters of credit related to various insurance contracts and foreign vendor commitments | Senior Secured Credit Facility
Commitments And Contingencies [Line Items]
Standby letters of credit for various insurance contracts and commitments to foreign vendors	$ 54,591	$ 56,267
Standby letters of credit related to various insurance contracts and foreign vendor commitments | Senior Secured Credit Facility | Maximum
Commitments And Contingencies [Line Items]
Expiration period for standby letters of credit	2 years