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Reconciliation of Tax Loss Carryovers, Credit Carryovers and Valuation Allowances (Detail) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Income Taxes |  |  |
Net Operating Losses and Tax Credits, Beginning balance | $ 18.2 | $ 14.6 |
Net Operating Losses and Tax Credits, Additions | 1.6 | 3.7 |
Net Operating Losses and Tax Credits, Reductions |  | (0.1) |
Net Operating Losses and Tax Credits, Ending balance | 19.8 | 18.2 | $ 14.6
Balance at Beginning of Year | 13.1 |  |
Balance at End of Year | 15.0 | 13.1 |
Valuation Allowance For Deferred Tax Assets |  |  |
Income Taxes |  |  |
Balance at Beginning of Year | 13.1 | 11.0 |
Valuation Allowances, Additions | 1.9 | 2.1 |
Valuation Allowances, Reductions | 0.0 | 0.0 | (0.2)
Balance at End of Year | $ 15.0 | $ 13.1 | $ 11.0

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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 Total of the deductions in a given period to allowances and reserves, the valuation and qualifying accounts that are either netted against the cost of an asset (in order to value it at its carrying value) or that reflect a liability established to represent expected future costs, representing receivables written off as uncollectible and portions of the reserves utilized, respectively. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 4 -Subparagraph (SX 210.12-09) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24092-122690 + Details
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- Definition Total of allowances and reserves, the valuation and qualifying accounts that are either netted against the cost of an asset (in order to value it at its carrying value) or that reflect a liability established to represent expected future costs, acquired in a business combination. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 4 -Subparagraph (SX 210.12-09) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24092-122690 + Details
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