TITLE: Reference for the fact that $SL_n(O_K)$ surjects onto $SL_n(O_K/I)$ for any ideal I
QUESTION [9 upvotes]: Let $\mathcal{O}_K$ be the ring of integers in an algebraic number field $K$ and let $I \subset \mathcal{O}_K$ be a nonzero proper ideal.  It is not hard to see that the map $\text{SL}_n(\mathcal{O}_K) \rightarrow \text{SL}_n(\mathcal{O}_K/I)$ is surjective.  For instance, $\mathcal{O}_K/I$ is a product of local rings, and over such rings the special linear group is generated by elementary matrices.  I need this theorem in a paper I am writing, and I'd rather not spend a paragraph proving it.  Does anyone know a good reference?

REPLY [5 votes]: Platonov-Rapinchuk is the canonical reference.
EDIT A less nuclear option (and one I should have mentioned in the first place is Morris Newman's Integral Matrices. I think chapter 7 and/or 9 have a(n elementary) proof.