וַיֵּ֕לֶךְ בְּכָל־הַדֶּ֖רֶךְ אֲשֶׁר־הָלַ֣ךְ אָבִ֑יו וַֽיַּעֲבֹ֗ד אֶת־הַגִּלֻּלִים֙ אֲשֶׁ֣ר עָבַ֣ד אָבִ֔יו וַיִּשְׁתַּ֖חוּ לָהֶֽם׃
And he walked in all the way that his father walked in, and served the idols that his father served, and worshipped them.
Read midrashic interpretation of II Kings 21:21: and classical rabbinic exegesis.