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Effective Income Tax Reconciliation (Parenthetical) (Detail) - $ / shares
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Income Tax Disclosure [Abstract]      
Basic earnings per share amounts of the benefit resulting from the "Technological preferred or Preferred Enterprise" status $ 0.68 $ 0.26 $ 0.31
Diluted earnings per share amounts of the benefit resulting from the "Technological preferred or Preferred Enterprise" status $ 0.66 $ 0.26 $ 0.30