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Common and Preferred Stock - Additional Information (Detail) - Entity [Domain] - USD ($)
$ / shares in Units, $ in Thousands
 6 Months Ended
Jun. 30, 2015
Dec. 31, 2014
Aug. 18, 2010
Class of Stock [Line Items]      
Common stock loaned under share lending agreement, shares 9,000,000 9,000,000  
Nominal lending fee $ 0.01    
Senior convertible notes due August 15, 2015      
Class of Stock [Line Items]      
Principal amount $ 100,000 $ 100,000 $ 100,000