|**Long-Term Debt (Tables)**                                                                  | 6 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
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|**Debt Disclosure [Abstract]**                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Schedule of Long-term Debt Instruments                                                       | Long-term debt consisted of the following as of:June 30, 2016December 31, 2015(in thousands)Senior notes:3.25% Convertible senior notes due 2016:Principal amount$—$115,000Unamortized discount—(1,852)Unamortized debt issuance costs—(208)3.25% Convertible senior notes due 2016, net of discount and unamortized debt issuance costs—112,9407.75% Senior notes due 2022:Principal amount500,000500,000Unamortized debt issuance costs(7,003)(7,563)7.75% Senior notes due 2022, net of unamortized debt issuance costs492,997492,437Total senior notes492,997605,377Revolving credit facility—37,000Total debt, net of discount and unamortized debt issuance costs492,997642,377Less current portion of long-term debt—112,940Long-term debt$492,997$529,437
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|                                                                                             | June 30, 2016                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|                                                                                             | (in thousands)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Senior notes:                                                                                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|3.25% Convertible senior notes due 2016:                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Principal amount                                                                             | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|Unamortized discount                                                                         | —                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|Unamortized debt issuance costs                                                              | —                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|3.25% Convertible senior notes due 2016, net of discount and unamortized debt issuance costs | —                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|                                                                                             |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|7.75% Senior notes due 2022:                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Principal amount                                                                             | 500,000                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Unamortized debt issuance costs                                                              | (7,003                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|7.75% Senior notes due 2022, net of unamortized debt issuance costs                          | 492,997                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Total senior notes                                                                           | 492,997                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|                                                                                             |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Revolving credit facility                                                                    | —                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|Total debt, net of discount and unamortized debt issuance costs                              | 492,997                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Less current portion of long-term debt                                                       | —                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|Long-term debt                                                                               | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                

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duration X- DefinitionTabular disclosure of long-debt instruments or arrangements, including identification, terms, features, collateral requirements and other information necessary to a fair presentation. These are debt arrangements that originally required repayment more than twelve months after issuance or greater than the normal operating cycle of the entity, if longer.
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