The SAFARI instrument is a far-infrared imaging Fourier transform spectrometer for JAXA's SPICA mission. Taking advantage of the low emission of SPICA's 5 K telescope, SAFARI will provide background-limited, Nyquist-sampled spectroscopic imaging of a 2'x2' field-of-view over 34-210 Î¼m, revolutionizing far-infrared astronomy. SAFARI's aggressive science goals drive the development of a unique detector system combining large-format Transition Edge Sensor arrays and frequency division multiplexed SQUID readout with a high 160x multiplexing factor. The detectors and their cold readout electronics are packaged into 3 focal plane arrays that will be integrated into SAFARI's focal plane unit. This paper presents the preliminary design concept for the SAFARI detector system. Index Terms- Astrophysics, Bolometers, Frequency division multiplexing, Superconducting devices, System-level design.