Idaho's state rate is modest by national standards, but it still adds up.
Idaho taxes capital gains as ordinary income at up to 5.8%. Combined with the federal 20% and the 3.8% net investment income tax, a seller at the top bracket can face up to 29.6% of the gain.
There's no separate, lower rate for capital gains in Idaho; the 5.8% top bracket applies the same way it would to wage income. See the full picture, recapture included, in the capital gains tax calculator.
Reinvest in a like-kind property under Section 1031 and the 29.6% combined bill doesn't come due at closing. Work through your own numbers in the 1031 exchange calculator, then get your exact deadlines from the timeline calculator.
The mechanics behind the Idaho figures above are covered in more depth in what is a 1031 exchange and how to defer capital gains with a 1031.