Leases (Summary of Lease Related Expenses) (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018	[1]
Finance lease, Amortization of asset		$ 210
Finance lease, Interest on lease liabilities		101
Sublease income		(217)
Net lease expense		88,197
Variable lease expense		7,200
Lease operating expense		131,696	$ 88,833
Property, Plant and Equipment [Member]
Operating lease	[2]	23,447
Lease operating expense		20,100
Asset Retirement Obligations [Member]
Operating lease	[2]	3,024
Lease operating expense		3,000
Lease Operating Expense [Member]
Operating lease	[2],[3]	58,523
Lease operating expense		12,000
Selling and General Expense [Member]
Operating lease	[2]	3,109
Lease operating expense		$ 1,100

[1] Reclassified to conform to current presentation (see Note A).

[2] Includes $12.0 million for Lease operating expense, $1.1 million for Selling and general expense, $20.1 million for Property, plant and equipment, net and $3.0 million for Asset retirement obligations relating to short-term leases. Expenses primarily relate to drilling rigs and other oil and gas field equipment.

[3] Includes variable lease expenses of $7.2 million primarily related to additional volumes processed at a gas processing plant.