Lease - Lease expense (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Lease expense
Fixed lease expense	$ 15,050	$ 30,025
Variable lease expense	1,726	3,695
Short-term lease expense	1,715	3,084
Total operating lease expense	18,491	36,804
Finance lease expense:
Amortization of ROU assets	2,836	5,727
Interest on finance lease liabilities	375	763
Total finance lease expense	3,211	6,490
Total lease expense	$ 21,702	$ 43,294
Rental expense under all operating leases			$ 128,600