STOCK PLANS (Details)		3 Months Ended
Jan. 24, 2019	Mar. 31, 2019
Dividends [Abstract]
Stock dividend percentage	5.00%
Dividends date declared		Jan. 24, 2019
Dividend date to be paid		Mar. 29, 2019
Dividends payable, date of record		Feb. 28, 2019

The percentage rate used to calculate dividend payments on stock.

No definition available.

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Namespace Prefix:	fnrn_
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- Definition

Date the declared dividend will be paid, in CCYY-MM-DD format.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4304-108586

+ Details

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- References

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
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- Definition

Date the dividend to be paid was declared, in CCYY-MM-DD format.

+ References

+ Details

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Data Type:	xbrli:dateItemType
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- Definition

Date the holder must own the stock to be entitled to the dividend, in CCYY-MM-DD format.

+ References

No definition available.

+ Details

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