Compensation Plans Non Stock-Based Compensation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net Profits Plan [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
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%
Total Cash Payments, Made or Accrued under Profit Sharing Plan	$ (54)	$ 6,608	$ 3,498
Cash Payments Made or Accrued under Profit Sharing Plan Related to Divested Property	2,753	24,349	3,789
Total net settlements under Profit Sharing Plan	$ 2,699	30,957	7,287
401K Plan [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent	60.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay, Employees Hired December 31, 2014 and Prior	6.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay, Employees Hired After December 31, 2014	9.00%
Defined Contribution Plan, Cost	$ 4,500	$ 5,400	$ 5,600