Neil, the others are right--you should first show the full content and not hide any of the content on the page like you're doing. Depending on the size of the content, though, you might consider why you're hiding the content in the first place, as you might need to create more pages on your site for that content. Adding the content to new pages on the site might be good for your users, and certainly will fix your problem.

When considering the content and indexing, though, if the content is in the page source code then it will be indexed. Google does know if it's hidden, though, as Googlebot, Google's crawler, is essentially a version of Google Chrome.