Leases - Supplemental balance sheet information (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Leases
Operating lease right-of-use assets	$ 708,122
Other current liabilities	233,658
Operating lease liabilities	477,711
Total operating lease liabilities	711,369
Property and equipment, gross	4,602,239	$ 4,928,675
Accumulated depreciation	(3,276,204)	(3,550,726)
Property and equipment, net	1,326,035	1,377,949
Other current liabilities	18,349
Other long-term liabilities	42,403
Total finance lease liabilities	$ 60,752	$ 66,984
Weighted Average Remaining Lease Term: Operating leases	3 years 8 months 12 days
Weighted Average Remaining Lease Term: Finance leases	3 years 1 month 6 days
Weighted Average Discount Rate: Operating leases	9.30%
Weighted Average Discount Rate: Finance leases	7.50%
Property and equipment [Member]
Leases
Property and equipment, gross	$ 224,454
Accumulated depreciation	(178,848)
Property and equipment, net	$ 45,606