Leases - Supplemental balance sheet information (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Leases
Operating lease assets	$ 244,317	$ 380,968
Other current liabilities	136,386	186,967
Operating lease liabilities	109,856	192,624
Total operating lease liabilities	$ 246,242	$ 379,591
Operating Lease, Liability, Statement of Financial Position [Extensible List]	us-gaap:OperatingLeaseLiabilityNoncurrent us-gaap:AccountsPayableCurrent	us-gaap:OperatingLeaseLiabilityNoncurrent us-gaap:AccountsPayableCurrent
Property and equipment, gross	$ 4,960,698	$ 5,141,928
Accumulated depreciation	(3,611,522)	(3,577,224)
Property and equipment, net	1,349,176	1,564,704
Other current liabilities	44,362	49,820
Other long-term liabilities	78,059	110,789
Total finance lease liabilities	$ 122,421	$ 160,609
Weighted Average Remaining Lease Term: Operating leases	3 years	2 years 10 months 24 days
Weighted Average Remaining Lease Term: Finance leases	2 years 9 months 18 days	3 years 3 months 18 days
Weighted Average Discount Rate: Operating leases	8.30%	8.70%
Weighted Average Discount Rate: Finance leases	9.80%	9.60%
Property and equipment [Member]
Leases
Property and equipment, gross	$ 398,875	$ 398,875
Accumulated depreciation	(288,195)	(251,073)
Property and equipment, net	$ 110,680	$ 147,802