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Income Taxes Income Taxes - Effective Tax Rates Differing From Prevailing Federal Corporate Income Tax Rates (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
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Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Reconciliation of Effective Tax Rates [Line Items] |  |  |  |  |  |  |  |  |  |  |
Tax on income from continuing operations at statutory rate |  |  |  |  |  |  |  |  | $ 57,232 | $ (99,488) | $ 36,759
Tax on income from continuing operations at statutory rate,tax rate |  |  |  |  |  |  |  |  | 21.00% | 35.00% | 35.00%
Tax-exempt interest |  |  |  |  |  |  |  |  | $ (6,850) | $ (6,004) | $ (1,561)
Tax-exempt interest, tax rate |  |  |  |  |  |  |  |  | (2.50%) | 2.10% | (1.50%)
Derivative, Gain (Loss) on Derivative, Net | $ (44,716) | $ 17,583 | $ 8,932 | $ 25,191 | $ 31,544 | $ 4,163 | $ 40,692 | $ (462) | $ 6,990 | $ 75,937 | $ (30,167)
Valuation allowance |  |  |  |  |  |  |  |  | $ 5,278 | $ 127,675 | $ 139,584
Valuation allowance, tax rate |  |  |  |  |  |  |  |  | 1.90% | (44.90%) | 132.90%
Foreign taxes |  |  |  |  |  |  |  |  | $ 10,494 | $ (17,742) | $ 26,183
Foreign taxes, tax rate |  |  |  |  |  |  |  |  | 3.90% | 6.20% | 24.90%
Effective Income Tax Rate Reconciliation, Prior Year Income Taxes, Amount |  |  |  |  |  |  |  |  | $ (60,077) | $ 36,124 | $ (171,687)
Effective Income Tax Rate Reconciliation, Prior Year Income Taxes, Percent |  |  |  |  |  |  |  |  | (22.00%) | (12.70%) | (163.50%)
Other, net |  |  |  |  |  |  |  |  | $ 959 | $ 2,013 | $ 1,431
Other, net, tax rate |  |  |  |  |  |  |  |  | 0.40% | (0.70%) | 1.40%
Income tax expense (benefit) |  |  |  |  |  |  |  |  | $ 5,134 | $ 44,464 | $ 30,709
Effective Income Tax Rate Reconciliation, Percent |  |  |  |  |  |  |  |  | 1.90% | (15.70%) | 29.20%
Income Tax Reconciliation Tax Bankruptcy Adjustments |  |  |  |  |  |  |  |  | $ (1,902) | $ 1,886 | $ 0
Effective income Tax Reconciliation Tax Bankruptcy Adjustments |  |  |  |  |  |  |  |  | (0.70%) | (0.70%) | 0.00%
Variable Interest Entity, Primary Beneficiary [Member] | Income Loss On Variable Interest Entities [Member] |  |  |  |  |  |  |  |  |  |  |
Reconciliation of Effective Tax Rates [Line Items] |  |  |  |  |  |  |  |  |  |  |
Derivative, Gain (Loss) on Derivative, Net |  |  |  |  |  |  |  |  | $ 504,628 | $ (152,194) | $ (515,564)
Variable Interest Entity, Primary Beneficiary [Member] | Currency Swaps [Member] | Income Loss On Variable Interest Entities [Member] |  |  |  |  |  |  |  |  |  |  |
Reconciliation of Effective Tax Rates [Line Items] |  |  |  |  |  |  |  |  |  |  |
Derivative, Gain (Loss) on Derivative, Net |  |  |  |  |  |  |  |  | 11,425 | (25,530) | 58,990
Variable Interest Entity, Primary Beneficiary [Member] | Interest Rate Swaps [Member] | Income Loss On Variable Interest Entities [Member] |  |  |  |  |  |  |  |  |  |  |
Reconciliation of Effective Tax Rates [Line Items] |  |  |  |  |  |  |  |  |  |  |
Derivative, Gain (Loss) on Derivative, Net |  |  |  |  |  |  |  |  | $ 493,203 | $ (126,664) | $ (574,554)

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