Leases (Summary of Lease Related Expenses) (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	[1]	Jun. 30, 2019	Jun. 30, 2018	[1]
Operating lease	$ 57,381			$ 115,904
Amortization of asset	210			420
Interest on lease liabilities	101			202
Sublease income	(422)			(639)
Net lease expense	93,514			181,711
Variable lease expense	6,600			13,800
Lease operating expense	137,132	$ 81,236		268,828	$ 170,069
Property, plant and equipment
Operating lease	32,115			55,562
Lease operating expense	28,700			48,800
Asset retirement obligations
Operating lease	0			3,024
Lease operating expense				3,000
Lease operating expenses
Lease operating expense	10,400			22,400
Selling and general expense
Operating lease	3,235			6,344
Lease operating expense	1,200			2,300
Other Operating Income (Expense) [Member]
Operating lease	$ 894			$ 894

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