If the idea was based on one of gamesas's properties, you could not publish it yourself. If you'd like more detail, send me a PM with the game you're talking about (don't send the idea itself!) and I'll tell you who to contact.
If it's a new idea about a brand-new property, we're not accepting those at this time.
If you post something on these public forums, it's fair game. We're not reading the forums with the specific intent of "ripping off" the content, but we do read the forums and try to get a general vibe of what people are talking about. I know we haven't openly discussed the design of V13, so many of the topics being discussed are different from the design direction we've already been working on. Some of the things being brought up are similar.
That points out something important. While we love the conversation and we love the feedback we've been hearing, we can't respond directly to ideas that have been posted. We don't want to be in a situation were someone is upset because they hear us (eventually) post about a game mechanic or bit of content that is similar to what they posted. Our designers are working full-time to create a game, it's extremely likely that design we've already written matches or is similar to something that gets posted here. There are pre-existing design concepts that everyone is building on. An idea can be simultaneously developed and is not necessarily unique to one individual.
We're not hiring designers at this time, but if you're interested, you can always prepare a CV and send one in at the appropriate time. I expect that we will be reaching out to the fan-base to get some of our design staff.
We plan on acknowledging the contributions of the community, at the appropriate time, but we don't have specific plans. I've got a few ideas on how to do so, and we'll reach out to community for more ideas.
Summary: If you're concerned about compensation or credit, don't post.