Leases - Components of Lease Expense (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Mar. 31, 2020	Mar. 31, 2020
Operating costs and expenses:
Operating lease expense	$ 9,375	$ 18,976
Short-term lease expense	7,594	17,550
Variable lease expense	3,198	6,807
Finance lease expense:
Amortization of ROU assets	606	1,213
Interest on lease liabilities	391	788
Less: sublease income	(7,121)	(16,725)
Total	$ 14,043	$ 28,609