You seem to be changing the caption of a content control. Is this intended? It seemed from the description of your problem that you simply wish to paste StrDetails at the location of the bookmark BM2. If you want to move the cursor to a bookmark location, you could use something like this:
Then, if you want to put that text on the next line after the bookmark, you could do something like this:
So if you replace this line:
with the three lines I've provided I think it should work.