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Redeemable Noncontrolling Interests - Additional Information (Detail) - Aipu Group
$ in Thousands
1 Months Ended 12 Months Ended
Sep. 30, 2017
shares
Dec. 31, 2017
USD ($)
Dec. 31, 2016
Dec. 31, 2015
Tranche
May 31, 2014
Redeemable Noncontrolling Interest [Line Items]          
Business acquisition, equity interests acquired         50.00%
Number of tranches | Tranche       3  
Business acquisition, equity interests held by non controlling interest holders maximum percentage of eligible shares to be put each year by option exercise right     11.00% 28.00%  
Number of shares transferred | shares 2        
Description of ownership after transfer of shares   However, as the Written Put Option outstanding is legally detachable and separately exercisable from the 50% minus one share of equity interest in Aipu Group held by the Company, the Written Put Option qualifies as a freestanding financial instrument as defined under ASC 480 is accounted for as a derivative liability pursuant to ASC 815.      
Ownership percentage after transaction   50.00%      
Floor          
Redeemable Noncontrolling Interest [Line Items]          
Financial and operational performance targeted amount used to compute put option exercise price   $ 700,000      
Ceiling          
Redeemable Noncontrolling Interest [Line Items]          
Financial and operational performance targeted amount used to compute put option exercise price   $ 800,000