Full Idea
An idealist should perhaps be a coherentist, but there seems to be no reason why the coherentist should be an idealist; the link between the two is all one-way.
Gist of Idea
Idealists must be coherentists, but coherentists needn't be idealists
Source
Jonathan Dancy (Intro to Contemporary Epistemology [1985], 9.5)
Book Reference
Dancy,Jonathan: 'Introduction to Contemporary Epistemology' [Blackwell 1985], p.137
A Reaction
I don't see why an idealist shouldn't be a rationalist foundationalist, with a private reality full of certainties founded on simple a priori truths. Personally I'm an empiricist coherentist, this week.