Leases (Schedule of lease costs) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)
Leases [Abstract]
Amortization of finance leased assets	$ 985
Interest on finance lease liabilities	111
Operating lease cost	598
Short-term lease cost	9,974	[1]
Variable lease cost	106
Total lease cost	11,774
Capitalized costs included in short-term lease costs	$ 5,700

[1] Short-term lease cost includes amounts capitalized related to our oil and natural gas segment of $5.7 million.