You should read to understand the author's argument. That doesn't just mean understanding the author's thesis but also the evidence/smaller arguments that the author uses to back up the thesis. You are wasting your time if you try to read for particular detail as a general understanding of the author's opinion and how to apply that opinion should answer a good majority of the questions.
That is true most of the case, but is certainly not always true for every single question. There are detail questions every once in awhile, but, in my opinion, detail really shouldn't be the focus when reading these passages. It simply takes too long and timing is key.