Compensation Plans (Details 5) (USD $)	12 Months Ended				3 Months Ended	12 Months Ended							1 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Minimum	Dec. 31, 2012 Maximum	Dec. 31, 2012 APO Incentive Plan Minimum	Dec. 31, 2012 APO Incentive Plan Maximum	Dec. 31, 2012 APO Reward Plan area award	Dec. 31, 2012 APO Reward Plan Full vesting date, November 4, 2011 award	Dec. 31, 2012 APO Reward Plan Full vesting date, August 9, 2012 award	Dec. 31, 2012 APO Reward Plan Full vesting date, May 5, 2013 award	Dec. 31, 2012 APO Reward Plan Full vesting date, June 1, 2013 award	Jan. 31, 2007 SWR Reward Plan well	Jan. 31, 2007 SWR Reward Plan Full vesting date, October 25, 2011
Non-Equity Award Plans
Subsequent revenues received by participants (as a percent)						99.00%	100.00%
Subsequent expenses paid by participants (as a percent)						99.00%	100.00%
Economic interests in specified wells drilled or acquired as part of the plan (as a percent)						5.00%	7.50%
Number of specified areas in which awards granted								13
Quarterly bonus amount, percentage of after-payout cash flow from wells drilled or recompleted, one								7.00%
Quarterly bonus amount, percentage of after-payout cash flow from wells drilled or recompleted, two								10.00%
Number of award fully vested									1	3
Number of awards with specified vesting date								13			3	6
Percentage of working interest in well													22.50%
Number of wells, working interest													1
Percentage of subsequent quarterly bonus amounts after full vesting date payable to participants														100.00%
Vesting period				2 years	5 years
Compensation expense recorded	$ (404,000)	$ 12,900,000	$ 13,900,000
Current liabilities:
Accrued liabilities and other	2,220,000	1,994,000
Non-current liabilities:
Accrued compensation under non-equity award plans	20,058,000	20,757,000
Total accrued compensation under non-equity award plans	$ 22,278,000	$ 22,751,000