Equity Investments - Summarized Combined Financial Data For Equity Investments - Balance Sheet Table (Details) - Western Gas Partners, LP [Member] - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Current assets	$ 220,912	$ 137,957
Property, plant and equipment, net	3,426,438	2,512,214
Other assets	35,411	36,373
Total assets	3,682,761	2,686,544
Current liabilities	80,109	80,490
Non-current liabilities	12,213	7,447
Equity	3,590,439	2,598,607
Total liabilities and equity	$ 3,682,761	$ 2,686,544