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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
	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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