Annual report pursuant to Section 13 and 15(d)

Income Taxes - Reconciliation of Statutory Federal Income Tax Amount (Details)

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Income Taxes - Reconciliation of Statutory Federal Income Tax Amount (Details) - USD ($)
3 Months Ended 12 Months Ended
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Income Tax Disclosure [Abstract]                      
Income (loss) before federal income taxes                 $ 436,961,000 $ (982,622,000) $ (1,480,885,000)
Expected income tax at statutory rate                 152,936,000 (343,918,000) (518,310,000)
State income taxes                 2,299,000 (5,883,000) (15,908,000)
Other differences                 5,731,000 4,293,000 (420,000)
Intraperiod tax allocation                 0 (1,349,000) 0
Remeasurement due to Tax Cut and Jobs Act                 190,034,000 0 0
Change in valuation allowance due to current year activity                 (158,704,000) 343,944,000 278,637,000
Change in valuation allowance due to Tax Cuts and Jobs Act                 (190,487,000) 0 0
Total income tax expense (benefit) provision $ (954,000) $ 2,763,000 $ 0 $ 0 $ 842,000 $ (3,407,000) $ (157,000) $ (191,000) $ 1,809,000 $ (2,913,000) $ (256,001,000)