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Convertible Notes (Details 2) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended
Mar. 31, 2012
Mar. 31, 2011
Dec. 31, 2011
Interest expense related to notes      
Amortization of discount at an additional effective interest rate $ 3,510 $ 3,016  
Total interest expense 6,580 5,988  
5% Convertible Senior Notes due 2014
      
Interest expense related to notes      
2014 Notes coupon interest at a rate of 5% 2,157 2,156  
Amortization of discount at an additional effective interest rate 3,510 3,016  
Total interest expense $ 5,667 $ 5,172  
Convertible notes stated interest rate (as a percent) 5.00% 5.00% 5.00%
Effective interest rate (as a percent) 11.70% 11.70%