The coronagraph instrument in the WFIRST-AFTA mission will allow high contrast imaging of exoplanetary systems with the benefit of a 2.4 meter space telescope. The instrument will feature an integral field spectrograph (IFS) capable of measuring spectra from exoplanets. Since the typical exoplanet target will be dimmer than the host star by a factor of ~1e9, and the dispersion of this light into many spectral channels further suppresses the photon rate, the noise requirements on the detector for this instrument will be very tight. From a performance perspective, many parameters are important, including the read noise, the dark current, and the clock induced charge. At the same time, from a functionality perspective, the unique challenges of the space environment, in particular damage from high energy cosmic rays, need to be assessed and mitigated. In this paper we present our recent work in selecting the detector for the WFIRST-AFTA IFS. We also discuss flight operation considerations and risks associated with these detectors as well as their technology readiness level.