Inhot pretty much covered it, and there's really nothing to add. The specifics of your clearance in this case, while vague, lie in the way you filed. If you filed to Boise via the VOR, then you could reasonably expect "Direct Boise" to indicate that you should fly to the VOR. However, in this case, it appears that you probably filed to the airport, as it's your destination.
If you filed to Boise Airterminal, then the clearance "Direct Boise" gives the airport as your clearance limit.
I get direct clearances like this all the time. In cases where the VOR or other navaid is colocated with the airport, it really doesn't make much difference until you're directly on top of the navaid. In Boise, the VOR is .8 nm SE of the airport, so it's not a big deal.
Generally when given direct to a VOR that might be confused with the airport, you'll hear "Direct Boise VOR."
As a sidenote, if on approaching Boise, you are "Cleared Approach, Boise," you may pick any approach, and your clearance limit becomes the missed approach fix (if provided) for the approach you select. If assigned a specific approach, your clearance limit in communication will be the missed hold or fix for the approach assigned.