Acquisitions - Impact to Historical Consolidated Statement of Income Table (details) (USD $) In Thousands, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012		Sep. 30, 2013	Sep. 30, 2012
Revenues	$ 278,001	$ 234,734	[1]	$ 762,874	$ 679,720	[1]
Net income	81,117	40,916	[1]	193,926	126,293	[1]
WGP Historical [Member]
Revenues		219,020			636,603
Net income		33,854			106,711
Non-Operated Marcellus Interest [Member]
Revenues		15,714			43,117
Net income		$ 7,062			$ 19,582

[1] Financial information has been recast to include the financial position and results attributable to the Non-Operated Marcellus Interest. See Note 2.