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Fair Value (Narrative) (Details) - Level 3 [Member] | 12 Months Ended
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Dec. 31, 2018 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
Impairments recorded on equity securities without readily determinable fair values | $ 0
Impairments recorded on goodwill and other acquisition intangibles | $ 0

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- Definition Equity Method And Other Investments Impairment + References No definition available. + Details
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Namespace Prefix: | isba_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- 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_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Total loss recognized during the period from the impairment of goodwill plus the loss recognized in the period resulting from the impairment of the carrying amount of intangible assets, other than goodwill. + References No definition available. + Details
Name: | us-gaap_GoodwillAndIntangibleAssetImpairment
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |