Annual report pursuant to Section 13 and 15(d)

Long-Term Debt - Future Maturities of Long-Term Debt (Parenthetical) (Detail)

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Long-Term Debt - Future Maturities of Long-Term Debt (Parenthetical) (Detail) - USD ($)
Dec. 31, 2017
Dec. 31, 2016
Debt Disclosure [Abstract]    
Premium/discount amounts $ 0 $ 1,258,000