Assets and Liabilities Measured at Fair Value - Nonrecurring Fair Value Measurements (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2017	[1],[2]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net Book Value Prior to Impairment		$ 57,690,000
Total Pretax Impairment	$ 0	20,000,000	[1],[2]	$ 0
Level 1 | United States Midland
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value impaired charges		0
Level 2 | United States Midland
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value impaired charges		0
Level 3 | United States Midland
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value impaired charges		$ 37,690,000

[1] ¹ Reclassified to conform with current presentation (see Notes C and E). 2017 revenue is presented net of $58.9 million of transportation, gathering and processing costs as historically shown prior to the adoption of ASC 606 on January 1, 2018. See Notes to Consolidated Financial Statements, page 58.

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