Assurance over XBRL is currently optional. The SEC does not require assurance over the XBRL being provided today, and has given companies two years' liability relief. The caveat is that filers must be able to demonstrate a "good faith" effort to provide XBRL versions of their 10K and 10Q filings that are "the same" as their official filings. That is where assurance comes in.
raas-XBRL is able to perform Agreed Upon Procedures reviews of your XBRL in accordance with the AICPA's SOP (Statement of Position 09-1 - "Performing Agreed Upon Procedures Engagements that address the Completeness, Accuracy, or Consistency of XBRL-Tagged Data") of April 2009. We await the release of the updated SOP due in "early" 2011.
Contact us for additional information on assurance engagements.