What was the difference between the Weighted Average Grant Date Fair Value of nonvested shares in 2019 and forfeited shares?
{"Nonvested at December 31, 2018": {"Number of Shares": 213337.0, "Weighted Average Grant Date Fair Value": 20.21}, "Vested": {"Number of Shares": -106610.0, "Weighted Average Grant Date Fair Value": 20.17}, "Forfeited": {"Number of Shares": -13885.0, "Weighted Average Grant Date Fair Value": 20.64}, "Nonvested at December 31, 2019": {"Number of Shares": 92842.0, "Weighted Average Grant Date Fair Value": 20.13}}
forfeited_weighted_avg_grant_date_fair_value = df["Forfeited"]["Weighted Average Grant Date Fair Value"]
nonvested_at_december_31_2019_weighted_avg_grant_date_fair_value = df["Nonvested at December 31, 2019"]["Weighted Average Grant Date Fair Value"]
answer = forfeited_weighted_avg_grant_date_fair_value - nonvested_at_december_31_2019_weighted_avg_grant_date_fair_value