Leases - Components of Lease Expense (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Leases [Abstract]
Operating lease expense	$ 4,987	$ 10,031
Short-term lease expense	9,552	20,713
Finance lease cost:
Total lease expense	14,539	30,744
Sublease income	$ 200	$ 400