Leases (Components of Lease Expense) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)
Operating lease expense	$ 3,781
Short-term lease expense	16,571
Lease expense, gross	20,352
Less: Sublease income	259
Total lease expense	$ 20,093
Maximum [Member]
Operating lease, remaining lease terms	10 years
Minimum [Member]
Operating lease, remaining lease terms	1 year