Leases - Lease expense (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019
Leases [Abstract]
Operating lease cost	$ 20,280	$ 62,316
Amortization of right-of-use assets	350	1,127
Interest on lease liabilities	14	54
Variable lease cost	4,532	14,013
Short-term lease cost	28,580	85,780
Sublease income	(1,915)	(5,258)
Total lease cost	$ 51,841	$ 158,032