Leases - Supplemental Balance Sheet Information (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Sep. 10, 2019
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets		$ 104,271	$ 144,330	$ 495,000
Other current liabilities		$ 56,856	$ 57,910
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]		Deferred Long-term Liability Charges	Deferred Long-term Liability Charges
Operating lease liabilities		$ 63,526	$ 84,795
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]		Operating lease liabilities	Operating lease liabilities
Total		$ 120,382	$ 142,705
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		$ 6,965,949	$ 7,261,038
Accumulated depreciation		(4,783,616)	(4,554,856)
Property and equipment, net		2,182,333	2,706,182
Other current liabilities		58,379	61,493
Other long-term liabilities		103,795	171,706
Total		$ 162,174	$ 233,199
Operating Lease, Weighted Average Remaining Lease Term		2 years 9 months 18 days	3 years 1 month 6 days
Finance Lease, Weighted Average Remaining Lease Term		3 years 1 month 6 days	3 years 9 months 18 days
Operating Lease, Weighted Average Discount Rate, Percent		4.20%	5.00%
Finance Lease, Weighted Average Discount Rate, Percent		10.40%	10.20%
Asset Impairment Charges		$ 356,418
Property and equipment [Member]
Lessee, Lease, Description [Line Items]
Property and equipment, gross		889,708	$ 890,598
Accumulated depreciation		(754,292)	(683,271)
Property and equipment, net		135,416	$ 207,327
NBIoT capitalized costs
Lessee, Lease, Description [Line Items]
Asset Impairment Charges	$ 253,000
NBIoT capitalized costs | Operating lease assets
Lessee, Lease, Description [Line Items]
Asset Impairment Charges		$ 26,556