Loans and Allowances for Loan Losses (Aging of Recorded Investment in Past Due Loans, incuding Nonaccrual Loans, by class)(Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	$ 17,203	$ 10,280
Past Due Loans And Leases Receivable Ratio Of Loans And Leases Receivable	1.80%	1.08%
Financing Receivable Recorded Investment 30 To 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	5,372	6,454
Past Due Loans And Leases Receivable Ratio Of Loans And Leases Receivable	0.56%	0.68%
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	11,831	3,826
Past Due Loans And Leases Receivable Ratio Of Loans And Leases Receivable	1.24%	0.40%
Commercial And Industrial Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	2,342	1,218
Commercial And Industrial Receivable [Member] \| Financing Receivable Recorded Investment 30 To 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	445	1,090
Commercial And Industrial Receivable [Member] \| Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	1,897	128
Commercial Real Estate Other Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	11,564	6,277
Commercial Real Estate Other Receivable [Member] \| Financing Receivable Recorded Investment 30 To 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	2,432	4,346
Commercial Real Estate Other Receivable [Member] \| Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	9,132	1,931
Residential Mortgage Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	1,410	1,576
Residential Mortgage Receivable [Member] \| Financing Receivable Recorded Investment 30 To 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	885	899
Residential Mortgage Receivable [Member] \| Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	525	677
Residential Home Equity Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	1,678	1,102
Residential Home Equity Receivable [Member] \| Financing Receivable Recorded Investment 30 To 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	1,419	32
Residential Home Equity Receivable [Member] \| Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	259	1,070
Consumer Personal Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Consumer Personal Receivable [Member] \| Financing Receivable Recorded Investment 30 To 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Consumer Personal Receivable [Member] \| Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Consumer Installment Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	116	8
Consumer Installment Receivable [Member] \| Financing Receivable Recorded Investment 30 To 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	116	8
Consumer Installment Receivable [Member] \| Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Consumer Other Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	12
Consumer Other Financing Receivable [Member] \| Financing Receivable Recorded Investment 30 To 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	1
Consumer Other Financing Receivable [Member] \| Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	11
Consumer Credit Card Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	93	87
Consumer Credit Card Financing Receivable [Member] \| Financing Receivable Recorded Investment 30 To 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	75	78
Consumer Credit Card Financing Receivable [Member] \| Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	$ 18	$ 9

NATIONAL BANK OF INDIANAPOLIS CORP 10-Q