The Primordial Inflation Polarization Explorer (PIPER) is a balloon-borne instrument that will probe the epoch of reionization and search for the signature of inflation through large angular scale measurements of the linear polarization of the cosmic microwave background in four frequency bands from 200 to 600 GHz. The sky is imaged on to two 32x40 pixel arrays of time-domain multiplexed Transition-Edge Sensor (TES) bolometers operating at a bath temperature of 100 mK to achieve background-limited sensitivity. Each kilopixel array is indium-bump-bonded to a 2D superconducting quantum interference device (SQUID) time-domain multiplexer (MUX) chip and read out by warm electronics. Each pixel measures total incident power over a frequency band defined by bandpass filters in front of the array, while polarization sensitivity is provided by the upstream Variable-delay Polarization Modulators (VPMs) and analyzer grids. We present measurements of the detector dark parameters including transition temperature, saturation power, thermal conductivity, and time constants. We also present a summary of the pre-flight characterization of the detector arrays in the fully integrated flight receiver, describe the optimization of the integrated readout parameters, and the overall pixel yield of the arrays.