SAFARI is an imaging Fourier Transform Spectrometer for 35–200 μm under development for flight on the Japanese IR-satellite SPICA (2018). The 3.25 m diameter actively cooled telescope (<6K) will provide a sky background limited signal, which implies that detectors will need to have an NEP of 3.5⋅10−19 W/√Hz in order not to be limiting the sensitivity. The instrument will utilize three TES-based detector arrays, covering the 2×2 arcmin field-of-view in three octaves of wave length. This contribution will present an overview of the detector sub-system, i.e.: the detector arrays and radiation coupling, the focal plane assembly, the amplification chain and the frequency-domain- multiplexed electronics. The focus will be on the implications on the system design of the readout under the stringent power dissipation, heat load, and weight limitations.