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Share-Based Compensation - Summary of Number of Awards Granted and Grand Date Fair Value (Detail) - $ / shares shares in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Deferred Tax Assets Valuation Allowance [Line Items] |  |  |
Grant Date Fair Value | $ 24.20 |  |
TSR Awards [Member] |  |  |
Deferred Tax Assets Valuation Allowance [Line Items] |  |  |
Number of awards granted in fair values, Shares | 46 | 101 | 36
Grant Date Fair Value | $ 29.84 | $ 9.38 | $ 28.61
ROIC Awards [Member] |  |  |
Deferred Tax Assets Valuation Allowance [Line Items] |  |  |
Number of awards granted in fair values, Shares | 53 | 101 | 36
Grant Date Fair Value | $ 24.20 | $ 11.31 | $ 25.16

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- Definition Number of equity instruments other than options outstanding, including both vested and non-vested instruments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(i) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(ii) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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