Leases - Components of lease expense (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Leases
Operating lease cost	$ 81,762	$ 162,048
Short-term lease cost	12,141	31,426
Amortization of right-of-use assets	3,805	9,913
Interest on lease liabilities	1,099	2,280
Total finance lease cost	4,904	12,193
Total lease costs	$ 98,807	$ 205,667