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Income Taxes (Details) - USD ($) | 12 Months Ended |  |  |
--- | --- | --- | --- | ---
Dec. 31, 2007 | Mar. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2014
Income Tax Disclosure [Abstract] |  |  |  |
Net operating loss carryforwards |  | $ 585,700,000 |  |
Valuation allowance |  | 0 | $ 0 |
Information regarding income tax examinations [Abstract] |  |  |  |
Amount of IRS assessment for unpaid taxes and penalties related to REMIC issue |  |  |  | $ 197,500,000
Estimate of federal interest that may be due |  | 209,700,000 |  |
Amount of payment made related to the IRS assessment on the REMIC issue | $ 65,200,000 |  |  |
Amount of IRS assessment for unpaid taxes and penalties related to disallowance of carryback of 2009 net operating loss |  |  |  | $ 261,400,000
Estimate of additional state income taxes and interest that may be due |  | 87,400,000 |  |
Total amount of unrecognized tax benefits |  | 143,700,000 |  |
Total amount of the unrecognized tax benefits that would affect our effective tax rate |  | 125,000,000 |  |
Unrecognized tax benefits, accrued interest |  | $ 52,900,000 | $ 52,000,000 |

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- Definition The amount of the IRS assessment for unpaid taxes and penalties related to the disallowance of the carryback of the 2009 net operating loss. + References No definition available. + Details
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- Definition The estimate of additional state income taxes and interest that may be due upon the resolution of the REMIC issue. + References No definition available. + Details
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- Definition The estimate of federal interest that may be due upon the resolution of the REMIC issue. + References No definition available. + Details
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- Definition The amount of the payment made to the United States Department of Treasury related to the IRS assessment on the REMIC issue. + References No definition available. + Details
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- Definition Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319 + Details
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- Definition Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32559-109319 + Details
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- Definition Amount of unrecognized tax benefits. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319 + Details
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- Definition The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319 + Details
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