An idea alone is very hard to copy unless you have deep expertise in that area and can quickly understand the problems it solves.

For example, you describe me an idea for some SaaS startup targeted at constructions companies. I have no clue about this industry, so no matter how well you describe it to me I simply can't judge it and definitely can't implement it.

Even if you are an expert on the target audience and their problems, the small details that make the difference, you can call it vision, are normally not part of the 'idea'.