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Fair Value Measurements - Additional Information (Detail) - USD ($) | Dec. 31, 2017 | Dec. 31, 2016
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Fair Value Disclosures [Abstract] |  |
Unamortized debt issuance cost | $ 987,000 | $ 1,141,000

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- Definition The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset. + 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 210.5-02.17) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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