Flights are available daily from the end of July through September 3, 2018, with no minimum stay required. Some itineraries may require an extended layover, usually in Seattle or Portland, but depend on your departure days they can be avoided.
As an example, I found seats departing DTW on Wednesday, August 15 and returning from ANC on Friday, August 24, 2018. You'll have the best luck finding tickets at this price in early to mid-August, which is perfect for summer travel.
Need a room up North? Here's what's available for the sample dates on Hotelwatchdog.