停止自定义验证器在每次击键时触发

I wrote a custom validator using MVC DataAnnotations and the jQuery unobtrusive javascript library. It's working great. The only problem I have now is that after the initial validation, if the user edit's the field, it's firing the validator on each keystroke. Since the validator hits a web service to validate the input, I'd prefer that it always just validate the input when the user moves off of the field or the form is submitted. Is there a way to change this behavior? Here's my code:I wrote a custom validator using MVC DataAnnota