Leases - Supplemental balance sheet information (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Leases
Operating lease right-of-use assets	$ 651,971
Other current liabilities	217,390
Operating lease liabilities	436,574
Total operating lease liabilities	653,964
Property and equipment, gross	5,010,891	$ 4,928,675
Accumulated depreciation	(3,378,394)	(3,550,726)
Property and equipment, net	1,632,497	1,377,949
Other current liabilities	18,466
Other long-term liabilities	37,657
Total finance lease liabilities	$ 56,123	$ 66,984
Weighted Average Remaining Lease Term: Operating leases	3 years 7 months 6 days
Weighted Average Remaining Lease Term: Finance leases	2 years 9 months 18 days
Weighted Average Discount Rate: Operating leases	9.10%
Weighted Average Discount Rate: Finance leases	7.50%
Property and equipment [Member]
Leases
Property and equipment, gross	$ 224,454
Accumulated depreciation	(182,653)
Property and equipment, net	$ 41,801