The Green Party has never been on the ballot in Idaho, although some of its presidential nominees have qualified as independent candidates. The Idaho independent petition is only 1,000 signatures for statewide office, but the party petition is 2% of the last presidential vote, which is currently 13,809.
However, the Green Party is now circulating a party petition in Idaho, and it has a few hundred signatures. The deadline is August 30. The reason the party petition deadline is so late is that the Populist Party won a lawsuit in the Ninth Circuit in 1984 against the old May deadline.
If a party can get on the ballot in Idaho, it can easily remain on the ballot, as long as it continues to be active. A party remains on the ballot if it runs at least three candidates every two years. It doesn’t matter how many votes its candidates get; it merely must run three candidates.