There is a big chunk of obfuscated document write (javascript) at the bottom of the script.

I have no idea what that is intended to do or why it would be obfuscated in that way or even if it is meant to be there. Since javascript is meant to be a plain language scripting language when obfuscated in this way I get suspicious at what they have to hide.

So it may well be a legit detection but you could submit it (as a possible false positive) for further analysis.