How to track who and when opened a document, from the document Library in SharePoint 2010?

We have a requirement to keep a track of all the documents opened from our intranet portal? Is it possible to do it OOTB or do we have to code for it?

The portal has many sites and subsites within it, in which there are multiple document libraries. We need to track across not all site's document libraries but to specific libraries of specific site on which document was opened by which user and timestamp.

Thanks,