Transactions with Affiliates and Other Related Parties (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
PDCM
Related Party Transactions:
Amount included in cost of natural gas marketing	$ 7.1	$ 4.7	$ 23.2	$ 12.5
Well operating and administrative services billed to PDCM	1.6	3.6	5.7	10.4
Affiliated Partnerships
Related Party Transactions:
Amount included in cost of natural gas marketing		$ 0.3		$ 0.9