PS. If you don't have an account in Bittrex yet, you should know that registration was disabled as of the moment.
Read more here: https://support.bittrex.com/hc/en-us/articles/215282838-Frequently-asked-questions-about-account-verification
What documents they mostly require? I am planning on moving to Bittrex for my trading because they've got a lot more coins than Polo (my current platform). Do you guys think this is good?
I would like to emphasize what fellow members recommended to you. Do not deposit to Bittrex until you are fully Verified. Take your time to go through verification. Thousands of traders suprisingly appeared in a situation that their account was restricted to withdraw overnight. Due to rapid increase of support tickets some traders still wait for their verification after several months.
Thank you so much for your advise guys! As for now, I am using Poloniex. And I am not verified there. Planning on shifting from Poloniex to Bittrex for Bittrex have a large number of coins currently supported.