Compensation Plans Compensation Plans: Non-stock Based (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Cash Bonus Plan [Member]
Accrued Cash Bonus Plan Expense	$ 23,900,000	$ 21,600,000	$ 7,800,000
Net Profits Plan [Member]
Minimum Percentage of Oil and Gas Wells, Costs Recovered for Payment to Employees from Net Profit Plan	100.00%
Percentage of Future Net Cash Flow Received by Participants from Net Profit Plan	10.00%
Percentage Of Future Net Cash Flow Received By Participants From Net Profit Plan Increased To	20.00%
Percentage of Oil and Gas Wells Costs Recovered for Additional Payment Employees from Net Profit Plan	200.00%
Cash Payments Made or Accrued under Profit Sharing Plan Allocated to General and Administrative Expense	19,326,000	19,798,000	18,399,000
Cash Payments Made or Accrued under Profit Sharing Plan Allocated to Oil and Gas Exploration Expense	2,091,000	2,633,000	1,463,000
Total Cash Payments, Made or Accrued under Profit Sharing Plan	21,417,000	22,431,000	19,862,000
Cash Payments Made or Accrued under Profit Sharing Plan Related to Divested Property	$ 6,300,000	$ 26,100,000	$ 700,000