Inferring common mode impedance for a given CMRR
CMRR is a ratio of Ad (differential mode gain) to Acm (common mode gain) which is 20log(Ad/Acm).  With a high CMRR you may imply that input impedance is high but I don't think you can calculate it directly from CMRR.  CMRR has more to do with the balance of the amplifier and its ability to reject, or not amplify, noise which is present at both (inverting and non inverting) inputs.