Derivative Instruments and Hedging Activities (Schedule of Derivative Instruments Outstanding) (Details) (USD $)	Sep. 30, 2012 bbl
October 2012 To November 2012 [Member] | Oil Contract [Member] | Fixed Price Swaps [Member]
Derivative [Line Items]
Daily Average Volume	2,921
Volume	178,200
Average Swap Price	$ 104.05
December 2012 [Member] | Oil Contract [Member] | Fixed Price Swaps [Member]
Derivative [Line Items]
Daily Average Volume	3,361
Volume	104,200
Average Swap Price	$ 102.80
January 2013 To July 2013 [Member] | Oil Contract [Member] | Fixed Price Swaps [Member]
Derivative [Line Items]
Daily Average Volume	5,703
Volume	1,209,000
Average Swap Price	$ 101.18
August 2013 To November 2013 [Member] | Oil Contract [Member] | Fixed Price Swaps [Member]
Derivative [Line Items]
Daily Average Volume	2,549
Volume	311,000
Average Swap Price	$ 102.11
December 2013 [Member] | Oil Contract [Member] | Fixed Price Swaps [Member]
Derivative [Line Items]
Daily Average Volume	3,306
Volume	102,500
Average Swap Price	$ 102.33
October 2012 To December 2012 [Member] | Oil Contract [Member] | Collars [Member]
Derivative [Line Items]
Daily Average Volume	1,000
Volume	92,000
October 2012 To December 2012 [Member] | Oil Contract [Member] | Collars [Member] | Minimum [Member]
Derivative [Line Items]
Average Swap Price	$ 87.50
October 2012 To December 2012 [Member] | Oil Contract [Member] | Collars [Member] | Maximum [Member]
Derivative [Line Items]
Average Swap Price	$ 123.18
October 2012 To December 2012 [Member] | Gas Contract [Member]
Derivative [Line Items]
Daily Average Volume	1,000
Volume	92,000
Average Swap Price	$ 2.69
January 2013 To December 2013 [Member] | Oil Contract [Member] | Collars [Member]
Derivative [Line Items]
Daily Average Volume	1,000
Volume	365,000
January 2013 To December 2013 [Member] | Oil Contract [Member] | Collars [Member] | Minimum [Member]
Derivative [Line Items]
Average Swap Price	$ 80.00
January 2013 To December 2013 [Member] | Oil Contract [Member] | Collars [Member] | Maximum [Member]
Derivative [Line Items]
Average Swap Price	$ 104.10
January 2013 To December 2013 [Member] | Gas Contract [Member]
Derivative [Line Items]
Daily Average Volume	1,000
Volume	365,000
Average Swap Price	$ 3.51
January 2014 To December 2014 [Member] | Oil Contract [Member] | Fixed Price Swaps [Member]
Derivative [Line Items]
Daily Average Volume	1,000
Volume	365,000
Average Swap Price	$ 100.20
January 2014 To December 2014 [Member] | Gas Contract [Member]
Derivative [Line Items]
Daily Average Volume	5,000
Volume	1,825,000
Average Swap Price	$ 4.01
Hilcorp Acquisition [Member] | November 2012 To December 2012 [Member] | Oil Contract [Member]
Derivative [Line Items]
Daily Average Volume	3,500
Average Swap Price	$ 111.75
Hilcorp Acquisition [Member] | November 2012 To December 2012 [Member] | Gas Contract [Member]
Derivative [Line Items]
Daily Average Volume	14,492
Average Swap Price	$ 3.13
Hilcorp Acquisition [Member] | January 2013 To December 2013 [Member] | Oil Contract [Member]
Derivative [Line Items]
Daily Average Volume	2,662
Average Swap Price	$ 108.60
Hilcorp Acquisition [Member] | January 2013 To December 2013 [Member] | Gas Contract [Member]
Derivative [Line Items]
Daily Average Volume	8,562
Average Swap Price	$ 3.51