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Common and Preferred Stock - Additional Information (Detail) - USD ($)
$ / shares in Units, $ in Thousands, shares in Millions
 9 Months Ended
Sep. 30, 2015
Oct. 23, 2015
Aug. 14, 2015
Dec. 31, 2014
Class of Stock [Line Items]        
Common stock loaned under share lending agreement, shares 9.0     9.0
Nominal lending fee $ 0.01      
Subsequent Event        
Class of Stock [Line Items]        
Returned shares of common stock under share lending agreement   9.0    
Senior convertible notes due August 15, 2015        
Class of Stock [Line Items]        
Principal amount $ 100,000   $ 32,100 $ 100,000