A theoretical non-pertubative treatment is developed to explain the dephasing of electrons in the electronic Mach-Zehnder interferometer via interaction with a near-by partitioned electronic channel, which acts as a "which path" detector. The resulting formula reproduces the recant experimental behavior of the MZI interference visibility. By fitting the model to the experimental results, it is shown that the visibility is strongly influenced by merely ~3 detecting electrons, hence it reflects the Non-Gaussian properties behavior of the detector shot-noise.