http://www.tomshardware.com/answers/id-2210400/4790k-temperatures.html
"The maximum junction temperature on Ivy Bridge was 105C but Intel reduced that a bit for Haswell, don't remember if it was 98C ot 102C but if you are going to overclock, you obviously do not want to get anywhere near that.
80C is a generally safe core temperature but at the upper end of what most overclockers feel comfortable with.
Less than 70C core temperature under load is a safe area many OCers like to be in - very low likelihood of causing any damage to the chip.
The 72C you read is the max package (IHS) temperature"~InvalidError
In short, the mid 70s you have are fine, as are the idle temps. if you were in the mid 80-90s I would start to worry. Personally, I think I idle over night around 26-30 on my 4790k. I haven't OCed yet but I don't think I've hit 65* underload on the CPU (GPU peaked at 72 once). I haven't had my cam software up in a few weeks to watch it though.