Business and Summary of Significant Accounting Policies - Cash and cash equivalents (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Business Description And Accounting Policies [Abstract]
Reserve requirement	$ 51.8	$ 44.8

Cash on hand or on deposit with the Federal Reserve Bank required to meet regulatory reserve and clearing requirements.

No definition available.

Name:	by_ReserveRequirementCashAndCashEquivalentsBank
Namespace Prefix:	by_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant