Annual report pursuant to Section 13 and 15(d)

Supplemental Oil and Gas Disclosures - Standardized Measure of Discounted Future Net Cash Flows (Details)

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Supplemental Oil and Gas Disclosures - Standardized Measure of Discounted Future Net Cash Flows (Details) - USD ($)
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Standardized Measure of Discounted Future Net Cash Flows        
Future cash inflows $ 1,818,400,000 $ 2,296,700,000 $ 7,258,500,000  
Production (691,500,000) (840,100,000) (2,224,500,000)  
Development (141,100,000) (161,400,000) (922,000,000)  
Dismantlement and abandonment (427,700,000) (471,800,000) (475,400,000)  
Income taxes 0 0 (948,400,000) [1]  
Future net cash inflows before 10% discount 558,100,000 823,400,000 2,688,200,000  
10% annual discount factor (79,800,000) (209,500,000) (985,400,000)  
Standardized measure of discounted future net cash flows $ 478,300,000 $ 613,900,000 $ 1,702,800,000 $ 1,674,600,000
[1] No future income taxes were estimated to be paid in 2016 and 2015 as our tax position has sufficient tax basis to offset estimated future taxes. State income taxes were disregarded due to immateriality.