Commitments and Contingencies (Narrative) (Details) - Standby letters of credit related to various insurance contracts and foreign vendor commitments - Senior Secured Credit Facility - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Commitments And Contingencies [Line Items]
Standby letters of credit for various insurance contracts and commitments to foreign vendors	$ 22,787	$ 54,591
Maximum
Commitments And Contingencies [Line Items]
Expiration period for standby letters of credit	2 years