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Income Taxes - Summary of Information Related to Interest and Penalties on Uncertain Tax Positions (Detail) - USD ($) $ in Millions | 12 Months Ended |
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Income Tax Disclosure [Abstract] |  |  |
Accrued interest payable | $ 0.8 | $ 0.5 | $ 0.6
Interest expense (income) | $ 0.3 | $ (0.1) |

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- Definition Amount of interest expense accrued for an underpayment of income taxes. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32718-109319 + Details
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