Cash and Due from Banks (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Cash and Due from Banks.
Required reserve balance	$ 4.3	$ 4.0
Clearing balance requirement		$ 2.8

Represents the clearing balance requirement established with the Federal Reserve Bank to use its services.

No definition available.

Name:	buse_ClearingBalanceRequirement
Namespace Prefix:	buse_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant