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Operating Segments (Narrative) (Details)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting [Abstract]
Percentage of reportable segments total assets and operating results, or more	90.00%	90.00%	90.00%

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- Definition

Percentage Of Reportable Segment, Assets And Operating Results

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No definition available.

+ Details

Name:	isba_PercentageOfReportableSegmentAssetsAndOperatingResults
Namespace Prefix:	isba_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

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- References

No definition available.

+ Details

Name:	us-gaap_SegmentReportingAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration