Yeah, 45 is a little hot for idle. However, I don't think 76 for a stress test is horrible. That is the worst situation for the CPU. Don't forget that Tdie is 90 for this CPU. You can't go higher than 90, so you still have 14 degrees to work with. If you don't push your computer to the edge all the time I wouldn't worry about the high end of the CPU temperature. If you are, it probably wouldn't be a bad idea to invest in a more robust cooler.
Back to the idle temperature being high. Before you go changing things, I would check a few things. First, check in your bios the CPU fan profile. It may need to run at a higher speed at lower temperatures. Also, the bios could be referencing the motherboard temperature, not the CPU temperature, for CPU fan control. I recommend switching to the CPU temperature to give it better control (if it isn't set that way already).
Finally, and I think the more likely culprit, is the case. You didn't list a model number, but you said "closed case". I'm guessing the case you have is similar to the PS10 than the PS15. The former has practically no openings in the front for airflow, whereas the latter has a mesh front to encourage airflow. That could be the biggest reason for the high idle temps. You could add a larger CPU cooler or more case fans, but I suspect the case is the limiting factor with your computer.
I hope that helps. My personal opinion is your configuration is fine if you are using your PC for gaming a few hours a day. However, if you're going to be pushing the PC for a long period of time daily, you may want to make some improvements.
