All I can say is that this looks like a tuberous type. Once the foliage turns yellow and dies away, carefully shake the soil away from the cyclamen-like tuber and keep cool and dry in a paper bag. Start it into growing again at the end of February by placing in a polythene bag with some very lightly moistened compost mixed with perlite (not soaking wet) and place in a dark warm spot such as an airing cupboard. After a week or so, very carefully check to see signs of growth Once a bud starts to develop on the top, pot up carefully and keep warm and in good light.

Thanks Fractal. The leaves look waxy, they are healthy and green, and it looks a lot like an Elektra/Electra to be - I don't know if that is tuberous or not. It's been in flower constantly since I got it in May. Is the only way to be sure to unpot it and look at the roots? I don't want to stop watering it if it's not tuberous.

The problem with Begonia's is that all species and types readily hybridise with each other, even ones belonging to different sections within the genus so there are many hybrids out there of mixed or inter-grading characteristics. I must say that this does still look tuberous but I think it wouldn't harm to investigate by very gently scraping back a little compost near the stem base to reveal a potential tuber.

I would still keep it watered and inside from now on anyway as it still looks like its going great guns. It will tell you when its ready to die back, if it ever does.