Equity Investments - Summarized Combined Financial Data For Equity Investments - Income Statement Table (details) (Western Gas Partners [Member], USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Western Gas Partners [Member]
Schedule of Equity Method Investments [Line Items]
Revenues	$ 548,629	$ 261,705	$ 199,764
Operating income	336,188	171,496	135,498
Net income	$ 333,705	$ 170,175	$ 133,987