Equity Investments - Summarized Combined Financial Data For Equity Investments - Balance Sheet Table (Details) - Western Gas Partners, LP [Member] - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Equity Method Investments [Line Items]
Current assets	$ 118,472	$ 154,937
Property, plant and equipment, net	2,626,466	2,716,078
Other assets	39,802	43,713
Total assets	2,784,740	2,914,728
Current liabilities	63,468	78,116
Non-current liabilities	6,662	9,072
Equity	2,714,610	2,827,540
Total liabilities and equity	$ 2,784,740	$ 2,914,728