Because Dictionary type is a reference type, you're not in bad situation here, but just for code clarity consider defining a new type, derived from
Dictionary> just to shorten the code you're writing and to make it easy readable. The class should look like this:
internal class MyWrapper : Dictionary>
Or if it's important for you to keep with
IDictionary, then go on with composite design by wrapping a
Dictionary> instance into the class which implements the
IDictionary> and just delegates all the methods to the wrapped Dictionary.