and look on the right-hand side, there's a "Visual Interpretation of the International Residential Code" for stairways & handrails you can download. Very handy document, with very clear explanations & pictures.
(I wonder if they'll cite Monticello for being non-compliant)
I think it should be not more than 37 inches (94 cm) nor less than 30 inches (76 cm) from the upper surface of the handrail to the surface of the tread