Unrecognized Stock Based Compensation Expense Related to Unvested Shares (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
April 2014 - December 2014	$ 400
2015	411
2016	255
2017	42
2018 & thereafter

Share-Based Compensation Arrangement by Share-Based Payment Award Expected Future Compensation Remainder of Year

No definition available.

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Share Based Compensation Arrangement by Share Based Payment Award Expected Future Compensation Year Five and Thereafter

No definition available.

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Data Type:	xbrli:monetaryItemType
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Share Based Compensation Arrangement by Share Based Payment Award Expected Future Compensation Year Four

No definition available.

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Namespace Prefix:	pbib_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Share Based Compensation Arrangement by Share Based Payment Award Expected Future Compensation Year three

No definition available.

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Namespace Prefix:	pbib_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Share Based Compensation Arrangement by Share Based Payment Award Expected Future Compensation Year Two

No definition available.

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Namespace Prefix:	pbib_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration