Loans Held for Sale (Details) (USD $)	6 Months Ended
Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
Residential loans held for sale, at fair value	$ 6,104,000	$ 5,836,000	$ 3,819,000
Finance leases held for sale	44,400,000
Proceeds from sale of loans	4,743,000	3,283,000
Loans charge-off	0
Commercial And Commercial Real Estate [Member]
Proceeds from sale of loans	4,900,000	3,300,000
Income from sale of loan	200,000
Commercial and commercial real estate loans held for investment	4,700,000	3,100,000
Purchased impaired loans	100,000
Recoveries		200,000
Proceeds from sale of loans held for sale	$ 0	$ 0

Purchased Impaired Loans, Held For Sale, Fair Value Disclosure

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Namespace Prefix:	onb
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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- Definition

Reflects a reduction in bad debt expense attributable to collections of loans and lease receivables which had previously been fully or partially charged off as bad debts.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 114
-Paragraph 20

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 7
-Subparagraph d
-Article 9

+ Details

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Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Reflects the amount of loans and leases that have been removed, or charged off, from both loan receivables and the reserve for credit losses, typically because they are considered to be not salvageable or have been purchased by unconsolidated collection entities.

+ References

+ Details

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- Definition

The net gain or loss resulting from a sale of loans, including adjustments to record loans classified as held-for-sale at the lower-of-cost-or-market and fair value adjustments to loan held for investment purposes.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents loans held-for-sale as presented on the statement of financial position which may include mortgage loans held-for-sale, finance receivables held-for-sale, or any other loans classified as held-for-sale which are due the Company as of the balance sheet date.

+ Details

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Balance Type:	debit
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- Definition

Mortgage loans to individuals not classified as held for investment but are held for sale to permanent investors. Permanent investors are enterprises that invest in mortgage loans for their own accounts. Examples of permanent investors are insurance companies, commercial or mutual savings banks, savings and loan associations, pension plans and real estate investment trusts. Mortgage loans exclude mortgage-backed securities which are considered a debt security.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 65
-Paragraph 1, 34

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher OTS
-Name Federal Regulation (FR)
-Number Title 12
-Chapter V
-Section 563c.102
-Paragraph 8
-Subparagraph h
-Subsection I

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The aggregate amount of loans receivable that will be sold to other entities. Includes mortgage and all other loans (collectively, loans) not classified as held for investment. Such loans are stated at the lower of cost or market (approximates fair value). Mortgage loans exclude mortgage-backed securities which are considered a debt security (other loan).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 65
-Paragraph 4, 5, 6, 7, 8, 9, 12, 17, 28, 29

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 65
-Paragraph 4

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Statement of Position (SOP)
-Number 01-6
-Paragraph 13
-Subparagraph d

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 7
-Subparagraph a
-Article 9

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher OTS
-Name Federal Regulation (FR)
-Number Title 12
-Chapter V
-Section 563c.102
-Paragraph 8
-Subparagraph h
-Subsection I

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The cash inflow from Sales of Loans Held For Investment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 95
-Paragraph 16
-Subparagraph a

+ Details

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Data Type:	xbrli:monetaryItemType
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- Definition

The cash inflow resulting from the sale of loans classified as held-for-sale, including proceeds from loans sold through mortgage securitization.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 102
-Paragraph 9

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 95
-Paragraph 3, 15, 16, 17, 22, 23, 147, 148, 149

+ Details

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