Property, Plant and Equipment - Schedule of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Cost	$ 19,303,389	$ 16,502,620
Property, plant and equipment, Net	9,969,743	8,432,133	[1]
Exploration and Production
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Cost	19,096,323	16,309,149
Property, plant and equipment, Net	9,875,727	8,329,514
Corporate and other
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Cost	207,066	193,471
Property, plant and equipment, Net	94,016	102,619
Mineral Rights
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Cost	508,526	512,025
Property, plant and equipment, Net	121,163	144,912
Administrative Assets and Support Equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Net	$ 24,698	$ 27,915

[1] Reclassified to conform with current presentation (see Note E)