Get-MailboxPermission shows user's first name and a number

Hello.

When I use "Get-MailBoxPermission - Identity mailbox@company.com | fl" it shows the User properly if the User is a group.

But, if the User is a person, it shows their first name and then a number. This is not useful.

How can I get this command to display the User as the user ID or something more useful than a first name and a number?

Thank you,

SkyRocketGuy