How to Getting SteamID64 ID with Steam Trade Url
Solution 1:
The formula to calculate SteamID64 from AccountID (partner ID) is:
(universe << 56) | (type << 52) | (instance << 32) | account_id
In your case:
(1 << 56) | (1 << 52) | (1 << 32) | 487364592
Result:
76561198447630320
For trade offers (partner ID), the values for universe, type and instance are always 1.
Other possible values can be found here: https://github.com/DoctorMcKay/node-steamid/blob/master/index.js#L2-L50