A little bit US centric, but the message is universal...

Looking only at time and cost of internal preparation of SEC (HMRC in case of UK) reports is a perfectly valid approach, and I agree that it's hard to get hard data since people, budget, solution, sampling techniques, and financial complexity differ widely.

However, in the first five years of a new reporting format, it is relevant to not just look at internal filing costs but also consider external filing solutions and their costs and performance.

For instance, what if external providers gave you a wide range of their solution charges (I don't think they will give you their actual costs.) Perhaps they could break it down between block-style notes and and for detailed notes.

XBRL is like any new business---early expert solutions tend to be cost-efficient vs. internal preparation (do-it-yourself). For instance, I would find it very costly and time-consuming to build or purchase my own electric generator, upgrade it continuously for safety and performance, haul in the logs or gasoline, etc. I've decided to pay the local electric company $83 per month for their service. I do lose some self-sufficiency, but I have made the decision that it is cheaper and better to have someone else do that.