Leases (Summary of Total Lease Cost) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Leases
Operating lease cost	$ 336,156	$ 320,480
Short-term operating lease cost	6,131	5,899
Variable operating lease cost	82,868	76,027
Sublease income	(4,790)	(4,112)
Total lease cost	$ 420,365	$ 398,294