. interest is payable semi-annually on march 15 and september 15 of each year , commencing september 15 , 2017 , and is approximately $ 22 million per year . the 2027 notes may be redeemed prior to maturity at any time in whole or in part at the option of the company at a 201cmake-whole 201d redemption price . the unamortized discount and debt issuance costs are being amortized over the remaining term of the 2027 notes