Hallam was 6 of 8 from the floor. Royce O'Neale chipped in eight points, six assists and five rebounds for the Pioneers (8-7, 4-1 Western Athletic), who closed the game on an 8-1 run.
Mike McChristian put Idaho ahead 48-47 on a layup with 1:35 to play, but Hallam's layup with 1:14 left gave Denver the lead back before Brett Olson, Cam Griffin and O'Neale each made two free throws to seal the victory.
Denver also won its only other games against Idaho, in 1965 and 1966.
Charles Matthews, who spent his freshman season at Kentucky, has picked Michigan as his transfer school, according to a source.
Chad Ford and Jeff Goodman offer their opinions on the surprises they're expecting at the NBA draft, with Ford believing there will be a lot of trade activity while Goodman thinks people will be surprised by potential draft spot of Marquese Chriss.
Louisville coach Rick Pitino said he doesn't "have time to figure out what" Kentucky coach John Calipari meant in recent comments that appeared to be a jab at the Cardinals' program.