There are a lot of reasons for this, I will direct you to these articles:
- https://money.stackexchange.com/questions/36706/why-can-the-institutional-ownership-of-shares-be-larger-than-100
- https://www.investopedia.com/ask/answers/07/institutional_holdings.asp
- https://www.quora.com/Why-is-the-institutional-ownership-of-Baidu-Inc-greater-than-100
I hope that helps. Let me know if you have any further questions.