What was the overall change in Net investment gains  on investments held in rabbi trust in 2019 from 2017?
{"Foreign currency transaction gains(losses)": {"2019": -1262, "2018": 2029, "2017": -548}, "Gains (losses) on derivative instruments not designated as hedges": {"2019": -674, "2018": -1751, "2017": 143}, "Net investment gains (losses) on investments held in rabbi trust": {"2019": 2379, "2018": -867, "2017": 1619}, "Other miscellaneous income (expense)": {"2019": -857, "2018": -1659, "2017": 44}, "": {"2019": -414, "2018": -2248, "2017": 1258}}
net_investment_2019 = df["Net investment gains (losses) on investments held in rabbi trust"]["2019"]
net_investment_2017 = df["Net investment gains (losses) on investments held in rabbi trust"]["2017"]
answer = net_investment_2019 - net_investment_2017