Could be there's corrupt recovery data that ID is running into on launch. Empty the InDesign Recovery folder in your user library caches.
Thanks Peter. I think the process you indicate was to re-name the Caches folder in the Library? I followed the instructions to rename the 'InDesign Recovery' file.
The application then loaded correctly. However, it 'hung' whenever I try to launch a document. After force-quitting, it then wouldn't reload.
I've repeated the process to re-name the InDesign Recovery file, and this situation repeats perfectly. It seems that the initial problem was resolved, but perhaps there is another/deeper/new problem? Welcome advice.
Success! Some further tinkering - a combination of re-naming the Caches folder; then deleting preferences during the restart of InDesign (holding down Cntl-Opt-Cmd-Shift during launch) seems to have restored order. I can open and work with documents again.