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Derivative Instruments (Narrative) (Details) - USD ($) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2020 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Derivative [Line Items] |  |  |  |
Net unrealized gains (losses) arising during the period |  | $ 99,193,000 | $ (8,570,000) | $ 0
Unrealized gain, after tax |  | 73,502,000 | (6,350,000) | $ 0
Pre-tax income |  | 2,800,000 |  |
Unamortized deferred net loss balance from previously terminated cash flow hedges |  | 40,000,000 |  |
Pre-tax gains included in interest income on cash flow hedges |  | 5,000,000 |  |
Collateral |  | 155,400,000 | 84,600,000 |
Variation margin, amount reducing derivative liability |  | 162,700,000 | 113,700,000 |
Foreign Exchange Forward |  |  |  |
Derivative [Line Items] |  |  |  |
Notional amount |  | $ 24,100,000 | $ 32,900,000 |
Cash Flow Hedging |  |  |  |
Derivative [Line Items] |  |  |  |
Net unrealized gains (losses) arising during the period | $ 9,800,000 |  |  |
Unrealized gain, after tax | $ 7,300,000 |  |  |

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- Definition Cash Flow Hedge Termination Gain (Loss) to be Reclassified within Twelve Months + References No definition available. + Details
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- Definition The estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121549185&loc=d3e80748-113994 + Details
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- Definition Amount of right to receive cash collateral under master netting arrangements that have not been offset against derivative liabilities. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 55 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226016-175313 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 8 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121590274&loc=d3e41678-113959 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (d)(2) -URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312 + Details
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- Definition Nominal or face amount used to calculate payment on derivative. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1B -URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5580258-113959 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1A -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5579245-113959 + Details
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