Summary of Significant Accounting Policies - Supplemental Cash Flows (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Accounting Policies [Abstract]
Operating cash flows used in operating leases	$ 291,535	$ 266,619
Operating cash flows used in financing leases (interest)	14,940	14,664
Financing cash flows used in financing leases	35,360	36,008
Operating lease modifications and reassessments	103,158	89,727
New operating leases (including acquisitions and sale-leaseback transactions)	$ 240,822	$ 173,635