What was the percentage change in Balance at December 31 between 2018 and 2019?
{"Balance at January 1": {"2019": 3649, "2018": 4670}, "Increase related to current year tax positions": {"2019": 2834, "2018": 55}, "(Decrease) increase related to prior year tax positions": {"2019": -10, "2018": 46}, "Decrease related to lapse in statute of limitation": {"2019": -1457, "2018": -1076}, "Decrease related to settlements with taxing authorities": {"2019": "\u2014", "2018": -46}, "Balance at December 31": {"2019": 5016, "2018": 3649}}
balance_2019 = df["Balance at December 31"]["2019"]
balance_2018 = df["Balance at January 1"]["2019"]
answer = (balance_2019 - balance_2018) / balance_2018 * 100.0