Are All Ideas Derived from Nature?

Reading David Hume’s Enquiry into Human Understanding.

His first chapter of the Enquiry is of the Origin of Ideas.

He separates thoughts into two categories- Ideas and Impressions, impressions being his term for stronger thoughts based directly on first person encounters. He then notes that even our most creative thoughts are:

no more than the faculty of compounding, transposing, augmenting, or diminishing the materials afforded us by the senses and experience.”

I agree with this.  

Hume proposes two arguments that will be sufficient to prove it. The first is to analyze thoughts and see if they resolve into simpler ideas we copied from a precedent feeling, and this is the one I am focused on in this post.  
In this first category he offers:

The idea of God, as meaning an infinitely intelligent, wise, and good being, arises from reflecting on the operations of our own mind, and augmenting, without limit, those qualities of goodness and wisdom. We may prosecute this enquiry to what length we please…. Those who would assert that this position is not universally true nor without exception, have only one, and that an easy method of refuting it; by producing that idea which, in their opinion, is not derived from this source.”

It strikes me that this may be an exception.

The most foundational doctrine of Christianity is the Yrinity. The conception of God as one God, and at the same time, three distinct and separate persons, is so incomprehensible, that it is considered literally incoherent by many. Even in the early Christian creeds, they were careful in their language to avoid contradictions, but we are also forced to admit that we have literally nothing similar in creation. There is no kind of object or metaphor we can call on that will accurately capture this most basic and fundamental nature of God.  

If it is true that human thoughts are derived from 1) impressions we get though nature, and 2) some repackaging of those materials, then the doctrine of the trinity would perhaps be an example of an idea that is NOT human in origin. This isn’t to say that all incoherent ideas are divine, but I do accept Hume’s premise that thoughts come from impression made on the senses, and if the trinity doesn’t fit that, he’s either wrong, or the idea comes from outside human understanding. I don’t believe he’s wrong.