Speaking to US TV presenter Barbara Walters on news show 20/20, Mariah said: "It felt like an unsafe work environment. Anytime anybody's reeling threats at somebody, you know, that's just not appropriate.
"Sitting there on the road with two babies, I'm not gonna take any chances, so yeah I did hire more security.
"For all the drama, I hope it helps the show."
But she said she and hip-hop star Minaj have now mostly patched up their differences.
"For me, ultimately this is about the contestants. I've been blessed with my dream (for) more than half my life so I want to help give that back to someone else."
There are still tensions underneath the surface though, with Nicki recently telling The Hollywood Reporter: "I can think of at least one other person that shows more cleavage and skin than me."
The new series of American Idol hits UK screens on 17 January, and will be shown on 5* this year.