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Share-based Payment Arrangements - Summary of Information About USIE Option Plans (Detail) - USIE option plans [member]
shares in Thousands
 12 Months Ended
Dec. 31, 2017
USD ($)
shares
Dec. 31, 2016
USD ($)
shares
Dec. 31, 2015
USD ($)
shares
Disclosure of terms and conditions of share-based payment arrangement [Line Items]      
Number of options, beginning balance | shares 25,933 29,695 34,159
Number of options, forfeited | shares     (84)
Number of options, exercised | shares (377) (3,762) (4,380)
Number of options, ending balance | shares 25,556 25,933 29,695
Number of options, exercisable, end of year | shares 25,556 25,933 28,106
Weighted average exercise price, Beginning balance | $ $ 2.2 $ 2.1 $ 2.1
Weighted average exercise price, Options forfeited | $     2.8
Weighted average exercise price, Options exercised | $ 1.9 2.0 1.9
Weighted average exercise price, Ending balance | $ 2.2 2.2 2.1
Weighted average exercise price, Options exercisable, end of year | $ $ 2.2 $ 2.2 $ 2.1