Xamarin.Forms.Device.Idiom issue on tablet

Hi,
I have to open my application in portrait mode in phones and landscape mode in tablets. I am using below code for changing screen orientation. Its working fine in android phone. But in samsung galaxy tab 2 (API Level 16) sometimes i am getting Xamarin.Forms.Device.Idiom =Phone instead of tablet.

if (Xamarin.Forms.Device.Idiom == Xamarin.Forms.TargetIdiom.Tablet) {
            RequestedOrientation = global::Android.Content.PM.ScreenOrientation.Landscape | global::Android.Content.PM.ScreenOrientation.ReverseLandscape;
        } else {
            RequestedOrientation = global::Android.Content.PM.ScreenOrientation.Portrait;
        }