Equity Investments - Summarized Combined Financial Data For Equity Investments - Income Statement Table (Details) - Western Gas Partners, LP [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule of Equity Method Investments [Line Items]
Revenues	$ 1,087,125	$ 703,424	$ 687,554
Operating income	733,802	435,735	428,454
Net income	$ 731,364	$ 434,749	$ 427,511