This paper proposes an efficient detection method of hierarchically-modulated data for an advanced terrestrial digital multimedia broadcasting (AT-DMB) receiver. Hierarchical modulation, where low-priority (LP) symbols are hierarchically added to the existing high-priority (HP) symbols, has been considered to be useful for increasing the data rate in AT-DMB systems. The distance between two neighboring LP symbols is limited by the noise margin of HP symbols and thus should be shortened to minimize the effect on the detection of HP symbols. To cope with the poor condition of LP symbols, we introduce a coherent detection method based on coded decision-directed (CDD) channel estimation (CE). CDD-CE may provide an accurate estimation result even under the infrequent pilot arrangement of the T-DMB system. Additionally, we propose a moving average (MA) method in frequency direction to reduce noise existing in the estimated channel coefficients. Simulation results show that the proposed method can be a good solution to successfully detect LP data.