Leases (Components of Lease Expense) (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Lessee, Lease, Description [Line Items]
Operating lease expense	$ 3,921	$ 7,702
Short-term lease expense	16,486	33,057
Lease expense, gross	20,407	40,759
Less: Sublease income	262	521
Total lease expense	$ 20,145	$ 40,238
Maximum [Member]
Lessee, Lease, Description [Line Items]
Short-term lease, lease term		1 year
Minimum [Member]
Lessee, Lease, Description [Line Items]
Short-term lease, lease term		1 month