I have had some very good insights

Okay, I have had some very good insights and I have shared them with my bosses. Each time they reply “Oh that’s too expensive”, “I’ll think about that”, or “No we can’t do that” ect. Then later, perhaps a week or so, they will “come up” with the same idea and implement it as their “own idea”. When I mention that it was, in fact, my idea first, they act all surprised and say “Really?, I don’t remember that.” How can I fight back with such dishonesty, without losing my job? Should I write everything down first, show it to them and then have a copy ready, for when they “come up” with “my” idea later? I guess I just answered my own question, but if I am missing something, please let me know. Sincerely, thank you for everything!! Melinda