Compensation Plans Compensation Plans: Non-stock Based (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Cash Bonus Plan [Member]
Cash Bonus Limit, Percent of Base Compensation	200.00%
Accrued Cash Bonus Plan Expense	$ 16,300,000	$ 23,900,000	$ 21,600,000
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	15,565,000	19,326,000	19,798,000
Cash Payments Made or Accrued under Profit Sharing Plan Allocated to Oil and Gas Exploration Expense	1,751,000	2,091,000	2,633,000
Total Cash Payments, Made or Accrued under Profit Sharing Plan	17,316,000	21,417,000	22,431,000
Cash Payments Made or Accrued under Profit Sharing Plan Related to Divested Property	$ 2,300,000	$ 6,300,000	$ 26,100,000