Telerik Date Picker Disable using JavaScript

Asslam-o-Alaikum
I have a telerik Rad Date Picker; i want to Disable it using JavaScript
if have Following Code
fucntion Dis()
{
var v = document.getElementByID('dpNow').Disabled = true;

}
<telerik:RadDatePicker id="dpNow" runat="server' />
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If i use Simple asp Text Box Control it's hide with the same code ; but if i use Telerik Rad Date Picker it can't hide
Some one help please it's urgent =======>>>>

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