I grew up in Lewiston and Coeur d'Alene - even in the Northern parts of the state, the weather is still pretty mild in winter. I'd say that if your coop is draft free you'll be fine without the insulation. I personally am a believer in insulating the coop, and I think there are plenty of folks out there with half a roll sitting in their basement that they'd LOVE to give to someone... so if it was me, I'd insulate. But if you don't, I still think you'll be okay. BUT - make sure your coop is draft free and leave a reasonable amount of vents open.
I live in Mass we have temps down in the single digits during the winter. This will be the first year my chickens will have an insulated coop. I just finished it today. You should be fine as long as they have water and a dry place to sleep