Acquisitions (Prize Acquisition) (Narrative) (Details) (USD $)	12 Months Ended			0 Months Ended	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Apr. 20, 2012 Prize [Member]	Dec. 31, 2013 Prize [Member]	Dec. 31, 2012 Prize [Member]	Dec. 31, 2011 Prize [Member] MMBoe
Business Acquisition [Line Items]
Date of acquisition					Apr. 20, 2012
Aggregate purchase price				$ 225,100,000
Effective date of acquisition					Jan. 01, 2012
Proved developed reserves							13.3
Cost associated with acquisition recorded in acquisition and transaction costs						1,100,000
Environmental liability				1,891,000
Total revenue	455,629,000	371,998,000	360,904,000			24,600,000
Operating expenses	$ 346,726,000	$ 301,657,000	$ 269,128,000			$ 8,300,000