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Short and Long-Term Debt - Short-Term Debt Additional Information (Detail) - USD ($) $ in Millions | 1 Months Ended | 12 Months Ended
--- | --- | ---
Feb. 28, 2015 | Dec. 31, 2017
Debt Disclosure [Abstract] |  |
Average month-end balance |  | $ 0.1
Maximum month-end balance | $ 0.2 |

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
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Balance Type: | na
Period Type: | duration

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- Definition For the form of debt having an initial term of less than one year or less than the normal operating cycle, if longer, average borrowings during the period. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition For the form of debt having an initial term of less than one year or less than the normal operating cycle, if longer, maximum month-end borrowings during the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(19)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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Balance Type: | credit
Period Type: | duration