There is no such thing as ideal keyword density, and there never has been. Even at its most primitive, Google's algorithm wasn't so stupid as to be fooled by people who used a particular word exactly 3.6% of the time, or any such artificial number.
Just write naturally, and make sure that it reads well. If it sounds spammy, it is spammy and you need to rein back on how many times you use the same words and phrases. If it doesn't mean anything to people who are not familiar with it, you probably need to use those terms a little bit more.