What is the "fideism" rejected by the Catholic Church? In philosophy, fideism seems to be used as a label to refer to epistemological approaches that tend to prioritize faith over reason.  And this makes sense; after all, "fideism" is just Latin for "faith-ism."

In the context of Catholic theology, fideism is a bad thing.  John Paul II warned against "a resurgence of fideism" (Fides et ratio) and Pius X links it to modernism in Pascendi Dominici Gregis.

But it turns out that "fideism" is actually a very vague term, particularly so because it is frequently used pejoratively by opponents of certain belief systems.  One person might be accused of fideism for believing that reason alone cannot demonstrate God's existence, while another might be accused of it for believing that reason alone cannot change a sinner's heart.

The Stanford Encyclopedia of Philosophy gets to the heart of it:


  Fideism claims that truths of a certain kind can be grasped only by foregoing rational inquiry and relying solely on faith. [source, emphasis added]


Using this language, my question is: What are the "truths of a certain kind" found in the fideism rejected by the Catholic Church?  

Put another way: According to Catholicism, in what matters is it legitimate to prioritize faith over reason?  For example, consider doctrines like:


the nature of the Trinity
The immaculate conception of Mary
The virgin birth of Jesus Christ
The descent of Jesus into Hades after his crucifixion
The real presence of Jesus in the Eucharist


Are these doctrines thought to be discernible exclusively or primarily through reason?  Or do they find their primary support in one's faith in the Scriptures and Tradition?

How does the Catholic Church define the fideism that it rejects?

I am particularly interested in direct quotes from papal encyclicals and official documents of the Vatican, particularly post-Vatican II.
Problematic fideism in Catholicism occurs when faith is exalted at the expense of reason. That is, when faith involves or requires irrationality. Doctrines such as the Trinity are beyond reason and accessible only to faith, but they do not entail a transgression of reason.  This can also occur in a lesser mode when appeals to faith downplay or undermine the role of reason.  For example, John Paul II warns against privileging faith in scripture over the rationality of tradition and the Magisterium:


  There are also signs of a resurgence of fideism, which fails to recognize the importance of rational knowledge and philosophical discourse for the understanding of faith, indeed for the very possibility of belief in God. One currently widespread symptom of this fideistic tendency is a “biblicism” which tends to make the reading and exegesis of Sacred Scripture the sole criterion of truth. In consequence, the word of God is identified with Sacred Scripture alone, thus eliminating the doctrine of the Church which the Second Vatican Council stressed quite specifically. Having recalled that the word of God is present in both Scripture and Tradition,73 the Constitution Dei Verbum continues emphatically: “Sacred Tradition and Sacred Scripture comprise a single sacred deposit of the word of God entrusted to the Church. Embracing this deposit and united with their pastors, the People of God remain always faithful to the teaching of the Apostles”.74 Scripture, therefore, is not the Church's sole point of reference. The “supreme rule of her faith” 75 derives from the unity which the Spirit has created between Sacred Tradition, Sacred Scripture and the Magisterium of the Church in a reciprocity which means that none of the three can survive without the others.76
  
  Fides et Ratio, 55


John Paul II goes some way towards defining fideism when he quotes Dei Filius of the First Vatican Council.  As noted above, problematic fideism is not the belief in the superiority of faith, but rather the belief that there can be a true divergence between faith and reason which results in a contradiction between the truths of faith and the truths of reason:


  “Even if faith is superior to reason there can never be a true divergence between faith and reason, since the same God who reveals the mysteries and bestows the gift of faith has also placed in the human spirit the light of reason. This God could not deny himself, nor could the truth ever contradict the truth”.65
  
  Fides et Ratio, 53