Exclude Disconnected Mailboxes in Powershell

I want to get a list of mailboxes but not include disconneced mailboxes, I did some searching tried the following command, but it does not work.  It returns all mailboxes, including disconneced ones.  What am I missing?

get-MailboxDatabase "Archives Database" |Get-MailboxStatistics |where-object{$_DisconnectDate -
eq $Null}| Sort totalitemsize -desc | Select-object displayname,Totalitemsize, itemcount