Goodwill and Other Intangible Assets - Narrative (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018	Jan. 03, 2018
Goodwill [Line Items]
Goodwill	$ 796,359,000		$ 796,359,000		$ 796,359,000
Impairment of intangible asset	0	$ 18,650,000	0	$ 18,650,000
Amortization expense	1,639,000	1,733,000	$ 3,277,000	$ 3,655,000
Useful life, customer relationship intangible assets			17 years
Estimated annual amortization expense	6,552,000		$ 6,552,000
Midstream Acquisition
Goodwill [Line Items]
Goodwill						$ 796,359,000
Other intangible assets						$ 128,781,000
Customer Relationships
Goodwill [Line Items]
Impairment of intangible asset		18,650,000
Customer Relationships | Midstream Acquisition
Goodwill [Line Items]
Impairment of intangible asset	$ 0	$ 18,650,000