Equity Investments - Summarized Combined Financial Data For Equity Investments - Balance Sheet Table (details) (Western Gas Partners [Member], USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Western Gas Partners [Member]
Schedule of Equity Method Investments [Line Items]
Current assets	$ 141,781	$ 186,690
Property, plant and equipment, net	2,814,336	2,676,531
Other assets	48,799	38,258
Total assets	3,004,916	2,901,479
Current liabilities	95,102	206,602
Non-current liabilities	22,615	34,012
Equity	2,887,199	2,660,865
Total liabilities and equity	$ 3,004,916	$ 2,901,479