Without encryption, if I can get your .mdf and .ldf (and any .ndf files) for a given database, then I can attach the database as long as I have the same version or newer of SQL Server. I don't even have to go through a restore process (just for clarification).
This is a known issue with administrators over the system where SQL Server is installed. Even if you remove their access from within SQL Server, if they are able to stop SQL Server (which they can as administrators), they can then get the files at rest. This is why TDE is so attractive: minimum performance hit and the files at rest are encrypted.
K. Brian Kelley