Leases (Schedule of lease costs) (Details) - USD ($) $ in Thousands		3 Months Ended	6 Months Ended
		Jun. 30, 2019	Jun. 30, 2019
Leases [Abstract]
Amortization of finance leased assets		$ 995	$ 1,980
Interest on finance lease liabilities		100	211
Operating lease cost		1,052	1,651
Short-term lease cost	[1]	12,038	22,012
Variable lease cost		84	190
Total lease cost		14,269	26,044
Capitalized costs included in short-term lease costs		$ 9,000	$ 14,700

[1] Short-term lease cost includes amounts capitalized related to our oil and natural gas segment of $9.0 million and $14.7 million, respectively.