Loans and ALLL (Summary of Defaulted TDRs) (Details) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2016 NumberofLoan	Jun. 30, 2015 USD ($) loan	Jun. 30, 2016 NumberofLoan	Jun. 30, 2015 USD ($) loan
Financing Receivable, Modifications [Line Items]
Number of Loans \| NumberofLoan	0		0
Residential, Junior Liens, Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| loan		1		1
Pre- Default Recorded Investment		$ 39		$ 39
Charge-Off Recorded Upon Default		39		39
Post- Default Recorded Investment		$ 0		$ 0

Financing Receivable, Modifications, Pre-Default, Recorded Investment

No definition available.

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Namespace Prefix:	isba_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
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- Definition

Number of financing receivables that have been modified by troubled debt restructurings within the previous 12 months and for which there was a payment default.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953682-111524

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Amount of investment related to financing receivables modified by troubled debt restructurings within the previous 12 months, for which there was a payment default.

+ References

+ Details

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

- Definition

Reflects the amount of the write-down related to a troubled debt restructuring.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=25495931&loc=d3e18845-111554

+ Details

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

- Details

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