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Income Taxes (Details 2) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Valuation and Qualifying Accounts Disclosure [Line Items] |  |  |  |  |
Income Tax Expense (Benefit) |  |  | $ 63,851 | $ 15,817 | $ (151,157)
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent |  |  | 35.00% | 35.00% | 35.00%
Changes in Valuation and Qualifying Accounts |  |  |  |  |
Charges Utilized | $ (21,527) |  |  |  |
Tax Valuation Allowance |  |  |  |  |
Changes in Valuation and Qualifying Accounts |  |  |  |  |
Balance at Beginning of Period |  | $ 50,911 | $ 23,529 | $ 20,717 | $ 193,874
Charged (Credited) to Operations |  |  | 0 | 0 | 0
Charged to Other Account |  |  | 5,855 | 2,812 | 1,299
Charges Utilized |  |  | 0 | 0 | (174,456)
Balance at End of Period | $ 50,911 |  | 50,911 | $ 23,529 | $ 20,717
2017 U.S.Tax Reform Member [Member] |  |  |  |  |
Valuation and Qualifying Accounts Disclosure [Line Items] |  |  |  |  |
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount |  |  | $ 20,700 |  |
Scenario, Forecast [Member] |  |  |  |  |
Valuation and Qualifying Accounts Disclosure [Line Items] |  |  |  |  |
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent |  | 21.00% |  |  |

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