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Debt - January 2017 Exchangeable Senior Notes - Additional Information (Detail) - Convertible Debt
 3 Months Ended
Jan. 20, 2017
USD ($)
d
$ / shares
Jan. 19, 2017
$ / shares
Mar. 31, 2017
USD ($)
shares
Mar. 31, 2016
USD ($)
Debt Disclosure [Line Items]        
Convertible senior notes, stated interest rate     3.50%  
Convertible notes, interest expense     $ 3,400,000  
Interest expense, contractual coupon interest     1,400,000  
Accrued interest on convertible note     0 $ 200,000
Non Cash        
Debt Disclosure [Line Items]        
Convertible notes, interest expense     2,000,000  
2017 Notes        
Debt Disclosure [Line Items]        
Convertible senior notes, principal amount $ 30,000,000   $ 30,000,000  
Convertible senior notes, stated interest rate 3.50%      
Convertible senior notes, due date 2047      
Convertible senior notes, repurchase price at option of the issuer 100.00%      
Net proceeds from offering $ 28,800,000      
Convertible senior notes, interest payable dates payable semi-annually in arrears on January 15 and July 15 of each year, beginning on July 15, 2017      
Convertible senior notes, payment start date Jul. 15, 2017      
Convertible senior notes, maturity date Jan. 15, 2047      
Convertible senior notes, percentage of premium initial exchange price   35.00%    
Convertible senior notes, total ADS into which the debt is exchangeable | shares     7,716,048  
Value of shares in excess of principal amount of Notes based on closing price     $ 5,300,000  
Convertible senior notes, redemption start date Jan. 19, 2021      
Convertible senior notes redemption, end date Jan. 15, 2047      
Convertible senior notes, mandatory exchange in whole or in part if daily VWAP equals or exceeds percentage of exchange price 130.00%      
Convertible senior notes, mandatory exchange in whole or in part if daily VWAP, stock trigger price | $ / shares $ 5.05      
Convertible senior notes, mandatory exchange in whole or in part if daily VWAP equals or exceeds percentage of exchange price, at least number of VWAP Trading days 20 days      
Convertible senior notes, mandatory exchange in whole or in part if daily VWAP equals or exceeds percentage of exchange price, in any number of VWAP Trading days | d 30      
Convertible senior notes, discount     1,200,000  
Convertible notes, carrying amount net of unamortized discount     28,800,000  
Convertible notes, interest expense     200,000  
Interest expense, contractual coupon interest     200,000  
Accrued interest on convertible note     200,000  
2017 Notes | Minimum        
Debt Disclosure [Line Items]        
Percentage of holders of principal amount required to issue notice on default 25.00%      
2017 Notes | Maximum | Non Cash        
Debt Disclosure [Line Items]        
Convertible notes, interest expense     $ 100,000  
2017 Notes | American Depositary Shares        
Debt Disclosure [Line Items]        
Convertible senior notes, exchange rate of ADS per $1,000 principal amount of notes 257.2016      
Convertible senior notes, initial exchange price | $ / shares $ 3.89 $ 2.88