Summary of Significant Accounting Policies - Supplemental Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Operating cash flows used in operating leases	$ 360,088	$ 338,059
Operating cash flows used in financing leases (interest)	19,942	21,031
Financing cash flows used in financing leases	47,829	58,033
Operating lease modifications and reassessments	143,382	108,023
New operating leases (including acquisitions and sale-leaseback transactions)	$ 370,011	$ 170,464