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Indebtedness - Additional Information (Detail) - USD ($) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2018 | Dec. 31, 2017
Debt Disclosure [Abstract] |  |
Interest capitalized during the period | $ 0 | $ 0

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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 Amount of interest capitalized during the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6450988&loc=d3e26243-108391 + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration