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Significant Accounting Policies - Impairment of Goodwill and Definite-Lived Intangible Assets (Details) - USD ($)		1 Months Ended	12 Months Ended
	Jan. 03, 2018	May 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Impairment			$ 473,045,000	$ 0	$ 0
Impairment of intangible assets			0	0	18,650,000
Midstream
Property, Plant and Equipment [Line Items]
Goodwill acquired during period	$ 796,359,000
Other intangible assets	$ 128,781,000
Customer Relationships
Property, Plant and Equipment [Line Items]
Impairment of intangible assets			$ 0	$ 0	18,650,000
Useful life, customer relationship intangible assets			17 years
Customer Relationships \| Midstream
Property, Plant and Equipment [Line Items]
Impairment of intangible assets		$ 18,650,000			$ 18,650,000
Useful life, customer relationship intangible assets		17 years
Midstream \| Operating Segments \| Maximum
Property, Plant and Equipment [Line Items]
Percentage of fair value in excess of carrying amount (less than)			10.00%