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Equity - Authorized Shares and Common Shares Issued and Fully Paid (Parenthetical) (Detail) - $ / shares
Dec. 31, 2017
Dec. 31, 2016
Sep. 08, 2008
Sep. 07, 2008
Disclosure Of Classes Of Share Capital [Abstract]        
Common shares par value $ 0.01 $ 0.01 $ 0.01 $ 0.01