Summary of Significant Accounting Policies - Supplemental Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accounting Policies [Abstract]
Operating cash flows used in operating leases	$ 93,645	$ 86,418
Operating cash flows used in financing leases (interest)	4,975	4,844
Financing cash flows used in financing leases	12,441	12,739
Operating lease modifications and reassessments	31,994	34,916
New operating leases (including acquisitions and sale-leaseback transactions)	$ 48,200	$ 110,609