asp.net mvc2验证类型double

[MetadataType(typeof(Deal_Validation))]
    public partial class Deal
    {
    }

    public class Deal_Validation
    {
        [Required]
        public string Title { get; set; }

        public double? EstValue { set; get; }
    }

如何验证EstValue(检查是否为double类型?)

谢谢