Property, Plant and Equipment Narrative - (Details) - USD ($) $ in Thousands		6 Months Ended			12 Months Ended
		Jun. 30, 2019	Jun. 30, 2018		Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Well Costs		$ 245,017	$ 185,596			$ 207,855	$ 155,103
Exploratory well costs capitalized more than one year		211,900
Proceeds from sales of property, plant and equipment	[1]	16,816	621
Gain (loss) on sale of assets		12	(118)	[1]
MP Gulf Of Mexico LLC | Petrobas America Inc
Property, Plant and Equipment [Line Items]
Noncontrolling ownership interest						20.00%
Athabasca Oil Corporation | Canadian Subsidiary
Property, Plant and Equipment [Line Items]
Cost of acquired assets, carried interest					$ 168,000
Carried interest paid		126,900
Montney Natural Gas Fields
Property, Plant and Equipment [Line Items]
Proceeds from sales of property, plant and equipment					414,100
Gain (loss) on sale of assets			$ 3,800		$ 187,000
Deferred gain on sale of property		116,800
Brunei
Property, Plant and Equipment [Line Items]
Exploratory well costs capitalized more than one year		57,200
Vietnam
Property, Plant and Equipment [Line Items]
Exploratory well costs capitalized more than one year		66,100
Gulf of Mexico
Property, Plant and Equipment [Line Items]
Exploratory well costs capitalized more than one year		61,300
United States
Property, Plant and Equipment [Line Items]
Exploratory well costs capitalized more than one year		$ 27,300
Kaybob Duvernay Lands, Alberta | Canadian Subsidiary
Property, Plant and Equipment [Line Items]
Interest in assets acquired					70.00%
Placid Montney Lands, Alberta | Canadian Subsidiary
Property, Plant and Equipment [Line Items]
Interest in assets acquired					30.00%

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