The company said it made market purchases on Thursday to acquire a portion of its $700m convertible five-year issue due in 2017.
Interest on the bonds is 1%. The company now holds 2.8% of the issue itself.
In September, it spent $79.1m on buying back its 3.5% 2014 series of convertible bonds.
After the deal, it owned 28.8% of the notes.
