What was the change in net income between Quarter Ended  September and December?
{"": {"December 31,": 2018.0, "September 30,": 2018.0, "June 30,": 2018.0, "March 31,": 2018.0}, "Sales, net": {"December 31,": 154161.0, "September 30,": 173082.0, "June 30,": 196032.0, "March 31,": 195617.0}, "Gross Profit": {"December 31,": 75188.0, "September 30,": 85539.0, "June 30,": 101235.0, "March 31,": 103645.0}, "Restructuring Expense": {"December 31,": 3836, "September 30,": 403.0, "June 30,": "$ \u2014", "March 31,": "$ \u2014"}, "Operating income": {"December 31,": 19570.0, "September 30,": 39862.0, "June 30,": 56018.0, "March 31,": 56103.0}, "Income from continuing operations, net of income taxes": {"December 31,": 19222.0, "September 30,": 35157.0, "June 30,": 46400.0, "March 31,": 46370.0}, "Loss (income) from discontinued operations, net of income taxes": {"December 31,": 188.0, "September 30,": -371.0, "June 30,": 5.0, "March 31,": 140.0}, "Net Income": {"December 31,": 19410.0, "September 30,": 34786.0, "June 30,": 46405.0, "March 31,": 46510.0}, "Income from continuing operations attributable to noncontrolling interest": {"December 31,": 4.0, "September 30,": 7.0, "June 30,": 44.0, "March 31,": 31.0}, "Net income attributable to Advanced Energy Industries, Inc.": {"December 31,": 19406.0, "September 30,": 34779.0, "June 30,": 46361.0, "March 31,": 46479.0}, "Continuing Operations: -- Basic earnings per share": {"December 31,": 0.5, "September 30,": 0.9, "June 30,": 1.18, "March 31,": 1.17}, "Continuing Operations: -- Diluted earnings per share": {"December 31,": 0.5, "September 30,": 0.9, "June 30,": 1.17, "March 31,": 1.16}, "Discontinued Operations: -- Basic loss per share": {"December 31,": "$  \u2014", "September 30,": -0.01, "June 30,": "$ \u2014", "March 31,": "$ \u2014"}, "Discontinued Operations: -- Diluted loss per share": {"December 31,": "$  \u2014", "September 30,": -0.01, "June 30,": "$ \u2014", "March 31,": "$ \u2014"}, "Net Income: -- Basic earnings per share": {"December 31,": 0.51, "September 30,": 0.89, "June 30,": 1.18, "March 31,": 1.17}, "Net Income: -- Diluted earnings per share": {"December 31,": 0.5, "September 30,": 0.89, "June 30,": 1.17, "March 31,": 1.16}}
net_income_dec = df["Net Income"]["December 31,"]
net_income_sep = df["Net Income"]["September 30,"]
answer = net_income_dec - net_income_sep