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Convertible Senior Notes - Narrative (Detail) - USD ($)
 3 Months Ended
Aug. 18, 2014
Mar. 17, 2014
Mar. 31, 2017
Mar. 31, 2016
Dec. 31, 2016
Debt Instrument [Line Items]          
Convertible senior notes, carrying value     $ 250,468,000   $ 249,994,000
Company share price     $ 18.81    
Convertible Debt [Member] | 2019 Notes [Member]          
Debt Instrument [Line Items]          
Equity component of the notes     $ 11,445,000    
Interest expense on debt     3,503,000 $ 3,503,000  
Additional non-cash interest expense     900,000 $ 876,000  
Convertible Debt [Member] | March 2019 Notes [Member]          
Debt Instrument [Line Items]          
Principal amount   $ 143,750,000 $ 143,750,000    
Coupon rate   5.50% 5.50%    
Proceeds from issuance of convertible senior notes   $ 139,037,000      
Convertible senior notes, carrying value     $ 141,768,000    
Unamortized discount     1,982,000    
Convertible Debt [Member] | August 2019 Notes [Member]          
Debt Instrument [Line Items]          
Principal amount $ 111,000,000   $ 111,000,000    
Coupon rate 5.50%   5.50%    
Proceeds from issuance of convertible senior notes $ 109,615,000        
Convertible senior notes, carrying value     $ 108,700,000    
Unamortized discount     2,300,000    
Conversion rate basis, principal amount     $ 1,000,000