Press the Windows+Up Arrow keys to Maximize the window. This should pop the entire InDesign document window to fullscreen on your laptop screen. Don't reduce it though, without hooking up to your external monitor unless you don't want to see it and go through this all over again. Alas, there's no exact equivalent in MacOS, but you can try Option+Spacebar keys and see if it works for your Mac laptop. It may, but it's more of a crapshoot.