I'm not sure I understand your question - if I do, I have no idea why your document is closing. Is it, really? If you're using a new-ish version of InDesign your open documents show up as tabs below your toolbar. You can grab those tabs with the mouse and drag them off of the tab-dock, at which point they become free-floating windows. It should be easy to drag stuff from one window to the other.
The behavior of open document windows within InDesign varies a bit from version to version, and is somewhat different on Macs versus Windows machines. If my suggestion doesn't work for you, could you describe it a bit more? Hopefully with some information about what version you're on, and what platform you're running it on. (Knowing the current state of the "Enable Floating Document Window Docking" checkbox in the "Interface" section of your Preferences might be helpful as well.)
Thank you for your timely response. My iMac/Mountain Lion is one month old.
I had Apple install CS6 and was not aware of the free floating window. This solved my dilemma.
Again, thank you so very, very much.