What was the percentage change in the total interest expense between 2018 and 2019?
{"Contractual interest expense": {"2019": 19471, "2018": 30323, "2017": 38825}, "Capitalized interest": {"2019": -232, "2018": -141, "2017": -154}, "Amortization of debt issuance costs": {"2019": 334, "2018": 511, "2017": 1390}, "Amortization of debt (premium) discount": {"2019": 1481, "2018": 1843, "2017": -788}, "Imputed interest on acquisition related obligations": {"2019": 57, "2018": 113, "2017": 159}, "Interest expense on capital leases": {"2019": 128, "2018": 233, "2017": 323}, "Total interest expense": {"2019": 21239, "2018": 32882, "2017": 39755}}
total_interest_expense_2019 = df["Total interest expense"]["2019"]
total_interest_expense_2018 = df["Total interest expense"]["2018"]
answer = ( total_interest_expense_2019 - total_interest_expense_2018 ) / total_interest_expense_2018 * 100.0