Replacing special chars in a string with a single unique char

Replacing special chars in a string with a single unique char

I have a string like so:
string inputStr = "Name*&^%LastName*#@";
The following Regex will replace all the special chars with a '-'
Regex rgx = new Regex("[^a-zA-Z0-9 - _]");
someStr = rgx.Replace(someStr, "-");
That produces an output something like: Name---LastName---
How do I replace '---' with a single '-' so the output looks like this:
Name-LastName
So the question is how do I replace all the special chars with a single '-'?
Regards.