The idea had never crossed my mind, but it should have.

I must admit that the idea did cross my mind.

The idea crossed my mind that he might already be dead.

But at that moment a crazy idea crossed his mind.

The idea of writing a book had never crossed my mind.

The same idea had crossed his mind while the painter was talking.

The idea had crossed his mind more than once to take advantage of that as well.

If the idea ever crossed her mind, she rejected it.

The idea that anyone would do such a thing never even crossed my mind until last night.

The idea must have crossed a lot of people's minds.