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Income Tax Matters - Reconciliation of Income Tax Provision based on Effective Income Tax Rate and Statutory Tax Rate (Parenthetical) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Reconciliation between income tax provision and statutory income tax provision: |  |  |
(Increase) decrease in federal valuation allowances | $ 0.0 | $ 0.1 | $ (1.7)
State and Local Jurisdiction |  |  |
Reconciliation between income tax provision and statutory income tax provision: |  |  |
(Increase) decrease in federal valuation allowances | (3.5) | 1.4 | (2.9)
State and tax expense (benefit) before adjustments | 1.3 | 3.8 | 4.5
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount | $ 3.7 | $ (0.7) | $ 0.9

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- Definition Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to increase (decrease) in the valuation allowance for deferred tax assets. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32687-109319 + Details
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- Definition Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations, attributable to increase (decrease) in the income tax rates. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 45 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=120406818&loc=d3e32059-109318 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32687-109319 + Details
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