Ideas are very simple by nature. They can be intuitively (most times immediately) understood by almost anyone. They are usually small, fitting rather snugly into the pores of the imagination. But from that small, easily discarded bit of mind-acorn rises the magnificent oak-structures of generations.
Simplicity is a foundation that ideas and genius have in common. It is the primordial reaction from which both evolved; it is the innocuous sun around which they both revolve. Entangled around this core, genius and the ideas it spawns does the most to ensure their separation is kept to a minimum.
Genius stays as close to the idea as possible: it accomplishes much with what seems so simple, so little; it can easily be overlooked. Genius unravels the obvious not-so-obvious that has extensive ramifications.
When what is done isn't so far from what it thought, when the elegance of a solution isn't primarily the complication of its execution; perhaps, just perhaps, genius is what you've got.