I have filled out I-134 and provided my own financial docs as well. But I often read that it's better if they can show they will cover their own expense. A little confused...
-It is enough. Many parents have got their visa financially supported by their kids in U.S.
In any case, what kind of bank statement do they need - CD certificates or a statement of the list of their CD/Savings accounts?
-Your parents do not need to provide the financial documents. The visa officer will not deny their applications just because of the your financial support for your parents' travel (not themself).