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	$ 27,759	$ 55,383
Finance lease expense:
Amortization of right-of-use assets	375	775
Interest on lease liabilities	83	171
Variable lease cost	774	1,389
Total lease expense	$ 28,991	$ 57,718