Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies (Supplemental Cash Flow Information) (Details)

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Summary of Significant Accounting Policies (Supplemental Cash Flow Information) (Details) - USD ($)
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Supplemental cash flow information:      
Interest paid, net of capitalized amounts $ 0 $ 0 $ 0
Income taxes paid 0 0 0
Cash paid for amounts included in the measurement of lease liabilities:      
Operating cash flows from operating leases 3,414,000 0 0
Investing cash flows from operating leases 32,529,000 0 0
Non-cash investing and financing activities:      
Change in accrued capital expenditures (31,475,000) (52,757,000) (39,532,000)
Change in asset retirement costs 13,559,000 8,730,000 (607,000)
Contingent consideration arrangement 8,512,000 0 0
ROU assets obtained in exchange for lease liabilities:      
Operating leases 66,914,000    
Financing leases 2,197,000    
Federal      
Supplemental cash flow information:      
Income taxes paid $ 0 $ 0 $ 0