One of the many SEO "cant give you a straight answer" questions
To be honest, keyword density doesnt really exist nowadays, writing for the user is much more worth your time.
I have one page thats ranks first out of 19.6 million results. The use of the main keyword is too much for my liking especially in the amount of content we have but I'm not touching it whilst it's remained first for all this time!
Usually what you'll find is the pages that have it too many times are compensating in some other fashion such as links.
As a rough rule the alleged ideal density is 3% or 3 times in every 100 words. But don't bust your gut trying to achieve this. Write pretty "normally" first, then go back an chuck in the keywords a couple more times where it makes sense.
Also use variations of the keywords (but not too different) as this helps and also makes the copy sound better.
Hope it makes sense!