.75% ( 4.75 % ) senior notes due 2021 ( the 201cnotes 201d ) at a price equal to 100% ( 100 % ) of the principal amount of the notes being redeemed and paid the premium of $ 5.1 million and accrued interest of $ 1.9 million . the redemption also resulted in a write off of $ 1.2 million of certain fees . following the partial redemption , $ 565.0 million aggregate principal amount of notes remained outstanding . interest expense , net for the year ended december 31 , 2018 was $ 270