Amount of contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer, net of valuation allowance for impairment of recognized servicing assets.

No definition available.

Name:	onb_LoanServicingRightsNet
Namespace Prefix:	onb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Loan Servicing Rights - Components of Loan Servicing Rights and Valuation Allowance (Parenthetical) (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	May 31, 2016	Dec. 31, 2015	Sep. 30, 2015
Servicing Assets And Liabilities At Fair Value [Line Items]
Loan servicing rights	$ 25,920		$ 10,468	$ 10,283
Anchor BanCorp Wisconsin Inc [Member]
Servicing Assets And Liabilities At Fair Value [Line Items]
Loan servicing rights		$ 15,300