We do have bike insurance (for the tourers), but that's not JUST for theft, it's also for damages.
We have never had our tourers stolen (knocks wood), but, for example, the very first year we went on a tour we went to New Zealand,
and the airport 'people' (term used loosely, not intended to anger readers) decided to mangle my girlfriends bike so very badly we had te get a new frame, and lots of 'accessories' (like crankset etc.).
luckily it happened on the way back.
The insurance paid for it, rather more than her insurance fee had been.
However, that insurance is just for Dutch people i think (
www.unigarant.nl) and not cheap: from memory it's about 12, 15 % of the value of the bicycle for 5 years, theft / damages.
It does however replace your stolen bike with a new one for the first three years and it just needs the bike to be locked (with a good lock).
During our holidays our bikes are mostly locked at night, but, standing free next to our tent.