John Gill's  Exposition of the Bible 

2 Kings 21:17

Now the rest of the acts of Manasseh, and all that he did, and his sin that he sinned, are they not written in the book of the chronicles of the kings of Judah?

Now the rest of the acts of Manasseh and all that he did,.... Both good and bad, for he repented, and was humbled, and did many good things afterwards, though not recorded in this book:

and his sin that he sinned; his idolatry:

are they not written in the book of the chronicles of the kings of Judah? in which were recorded the most memorable events of their reigns; and in the canonical book of Chronicles are many things concerning Manasseh, which are not written here; see 2 Chronicles 33:11.