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Convertible 3.75% Senior Notes (Details Textual) - USD ($)
3 Months Ended
Dec. 22, 2014
Mar. 31, 2017
Mar. 31, 2016
Dec. 16, 2014
Debt Instrument [Line Items]        
Debt issuance costs   $ 3,000,000 $ 3,800,000  
Qualified Institutional Buyers        
Debt Instrument [Line Items]        
Face amount of the Notes $ 18,750,000.00     $ 125,000,000
Convertible Notes Payable        
Debt Instrument [Line Items]        
Stated interest rate   3.75%   3.75%
Net proceeds from sale of the Notes 139,000,000      
Underwriting fees and other related expenses $ 4,800,000      
Accrued interest   $ 1,600,000    
Conversion price (in dollars per share)   $ 11.29    
Initial conversion rate per $1,000 principal (in shares)   88.5716    
Conversion conditions, stock price (greater than)   130.00%    
Conversion conditions, trading price (less than)   98.00%    
Remaining term of the debt   2 years 9 months