Variable Interest Entities (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended	12 Months Ended
	Jul. 31, 2016	Mar. 31, 2019	Dec. 31, 2018
Variable Interest Entity [Line Items]
Acquisitions and capital investments		$ 127,910	$ 127,899
Earnings in equity investments		24,585	23,144
Distributions received		(41,236)	(36,578)
Maximum exposure to loss		111,259	$ 114,465
Carnero Gathering, Joint Venture
Variable Interest Entity [Line Items]
Payments to acquire interest in joint venture	$ 37,000	123,900
Debt incurred		$ 0