Leases (Summary of Lease Related Expenses) (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	[1]	Sep. 30, 2019	Sep. 30, 2018	[1]
Operating lease	$ 62,260			$ 178,164
Amortization of asset	0			420
Interest on lease liabilities	0			202
Sublease income	(395)			(1,034)
Net lease expense	118,693			300,404
Variable lease expense	9,000			22,800
Lease operating expense	147,632	$ 83,751		416,460	$ 253,820
Property, plant and equipment
Operating lease	53,117			108,679
Lease operating expense	37,400			86,200
Asset retirement obligations
Operating lease	0			3,024
Lease operating expense				3,000
Lease operating expenses
Lease operating expense	10,900			33,300
Selling and general expense
Operating lease	2,700			9,044
Lease operating expense	1,000			3,100
Other Operating Income (Expense) [Member]
Operating lease	$ 1,011			$ 1,905

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