Reporting on leaked documents is not a crime. Providing financial, sexual, or other incentives for leaked documents could be a crime. Publishing certain parts of leaked documents (i.e. reporting on a major breach of 1 million social security numbers, by publishing all of the leaked numbers; or reporting the Nintendo breach by posting Nintendo's source code), could be a crime or civil issue on a circumstantial basis.
For groups like Wikileaks, it helps that US government documents and laws, with limited exceptions, are not copyrighted or copyrightable in the US. So when they report a huge NSA scandal and publish those documents, the government can't claim copyright infringement... but they will tear the place apart to find the leaker. And of course, spy on the reporter extremely closely for any possible legal slip-up no matter how small (or, arguably, if they hate the reporter enough, make something up).
For groups like Wikileaks, it helps that US government documents and laws, with limited exceptions, are not copyrighted or copyrightable in the US. So when they report a huge NSA scandal and publish those documents, the government can't claim copyright infringement... but they will tear the place apart to find the leaker. And of course, spy on the reporter extremely closely for any possible legal slip-up no matter how small (or, arguably, if they hate the reporter enough, make something up).