how to find Running Count of String Column?

Hi Members,

I'm a new bee in SQL and would request your support for the below requirement.

below are the columns I have in table Customers.

Date	CustomerID
7/14/2015	AAA
7/14/2015	BBB
7/15/2015	AAA
7/15/2015	BBB
7/15/2015	CCC
7/16/2015	AAA
7/17/2015	AAA
7/18/2015	AAA
7/19/2015	AAA

What I need is to find running sum of count of customerIDs. here CustomerID is string.

so, the expected result is

Date	Run_Sum
7/14/2015	2
7/15/2015	5
7/16/2015	6
7/17/2015	7
7/18/2015	8
7/19/2015	9

It would be great if you can share the query.

Thanks,

Dhamu13