Leases - Supplemental Balance Sheet Information (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets	$ 725,605
Other current liabilities	237,533
Operating lease liabilities	491,842
Total	729,375
Property and equipment, gross	5,308,778	$ 5,688,678
Accumulated depreciation	(3,445,611)	(3,760,498)
Property and equipment, net	1,863,167	1,928,180
Other current liabilities	18,349
Other long-term liabilities	42,403
Total	$ 60,752	$ 66,984
Operating Lease, Weighted Average Remaining Lease Term	3 years 8 months 12 days
Finance Lease, Weighted Average Remaining Lease Term	3 years 1 month 6 days
Operating Lease, Weighted Average Discount Rate, Percent	9.30%
Finance Lease, Weighted Average Discount Rate, Percent	7.50%
Property and equipment
Lessee, Lease, Description [Line Items]
Property and equipment, gross	$ 224,454
Accumulated depreciation	(178,848)
Property and equipment, net	$ 45,606