Can't speak for the original poster, but at this point Postgres is a very capable and performant document-store database as well with the addition of the JSONB type and associated indexing and modification (in 9.5) functions. It's also more mature, has generally better durability than MongoDB, and it is easy to fall back/extend into relational queries on your document-store data if need be.

IMHO, unless you have a situation such that Mongo's horizontal scaling is actually required, it's better to use Postgres even if you're doing document-store stuff.