Need to check traffic sources

Hi all. Could anyone tell what are the tools would be perfect for the traffic analytics? First of all, I'm interesting in competitors traffic sources - how can I check it? For example, I tried to use semrush, but I can't find what I searched for. And I need something like that:
Competitor: example.com
Traffic sources:
1. source1.com - 15 000 visitors/50% site traffic
2. source 2.com - 15 000 visitors/50% site traffic
Or something like that. It would be great if anyone can help me.

SimilarWeb has something similar, however you need to have in mind, that these are just estimations.

There is no chance to get accurate info, just estimates.

Thanks guys, of course I know such tools as SimilarWeb and so on, but they don't gives even estimate info. Of course I know that the best way is using Google Analytics, but not for the competitors

See the semrush screenshot of the amazon traffic sources: http://prntscr.com/it9akz

As you can see, semrush gives an estimate info, so are any similar tools that gives similar information?

You cannot get every detail that you may be after, but semrush and the likes can offer you the best they could.

I suggest SimilarWeb, too. I've been using it for more or less 5 months now and though I'm not getting extremely detailed data, it's working well for me.