IDEA is a professional organization, rather than a certifying agency. They do have a list of certifications on their site that you can use to compare various options.
There are many places that offer group exercise certifications. I have ACE, and have always found it recognized wherever I go. It would not let you teach the programs that copyright a name, such as zumba, or one of the Les Mills things, but it would let you teach cardio, step, core, strength and conditioning, …. lots of options. You already have Pilates, which is a great specialty to have, so the group ex would be really helpful to spice things up, and to allow you to do blended individualized styles.
Whichever one you decide to use I would suggest strongly considering doing one that is NCCA accredited. That is a standard I have seen before for employment.
Here is a link to that IDEA comparison tool: