Idumeans also known as Red Jews are the descendants of Edomites forcibly converted to Judaism by John Hyrcanus around 100BC when he ordered the entire population to be enslaved and then freed. Hence they are also known as Ercolians or Hyrcanian Jews. Although they accept the Mishna they do not have a very sophisticated understanding of Judaism and are comparable to Samaritans, Falashahs and Karaites. They worked hard to make Hagarim and Toshavim out of all the gentiles of the Middle East such as for example the Elagabalites.
The Idumeans made a treaty with the house of Sassan in 632. The house of Sassan were allowed to place Yazdegard on a throne controlled by Idumeans and their Pahlavi Hagarim. Karaite Jews conquered the Idumeans in 636 causing but the Sassanians so the Pahlavis defended themselves but were suppressed again in 636 by Umar who got the Idueans on his side by arranging a marriage between Yazdegard's daughter and the house of Ali to rule after Yazdegard which they eventually did when Yazdegard died in 651.
The Idumean rulers were forced to accept the Anno Hegira as they began to be conquered one by one by Abdul Malik from 692AD.