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Income Tax Matters, Narrative (Details) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2018 | Mar. 31, 2017
Income Tax Disclosure [Abstract] |  |
Income tax provision | $ 5.9 | $ 18.5
Effective tax rate (percent) | 18.60% | 34.00%
Effective Income Tax Rate Reconciliation, Share-based Compensation, Excess Tax Benefit, Amount | $ (1.8) | $ (1.6)
Effective Income Tax Rate Reconciliation, Share-based Compensation, Excess Tax Benefit, Percent | (5.60%) | (2.90%)
Effective tax rate reconciliation, decrease to the valuation allowance for certain state net operating losses | $ 0.8 | $ 0.4
Effective tax rate reconciliation, decrease to the valuation allowance for certain state net operating losses (percent) | 2.70% | 0.80%
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Amount | $ 0.6 |
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Percent | 1.90% |
Gross unrecognized tax benefits | $ 1.5 |
Gross unrecognized tax benefits that would impact effective tax rate | $ 0.4 |

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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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