FAIR VALUE MEASUREMENTS - Financial instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Financial assets:
Securities available for sale (“AFS”), at fair value	$ 449,302	$ 400,144
Carrying Amount
Financial assets:
Cash and cash equivalents	182,059	249,526
Certificates of deposit in other banks	19,305	993
Securities available for sale (“AFS”), at fair value	449,302	400,144
Other investments	24,072	17,997
Loans held for sale	2,706	1,639
Loans, net	2,559,779	2,153,028
BOLI	78,140	66,310
MSR asset	5,919	3,749
Financial liabilities:
Deposits	2,954,453	2,614,138
Long-term Debt, Fair Value	67,629	77,305
Estimated Fair Value
Financial assets:
Cash and cash equivalents	182,059	249,526
Certificates of deposit in other banks	19,310	993
Securities available for sale (“AFS”), at fair value	449,302	400,144
Other investments	24,072	17,997
Loans held for sale	2,753	1,662
Loans, net	2,593,110	2,139,322
BOLI	78,140	66,310
MSR asset	8,420	6,347
Financial liabilities:
Deposits	2,956,229	2,614,995
Long-term Debt, Fair Value	66,816	75,923
Level 1 \| Estimated Fair Value
Financial assets:
Cash and cash equivalents	182,059	249,526
Certificates of deposit in other banks	0	0
Securities available for sale (“AFS”), at fair value	0	0
Other investments	3,375	2,650
Loans held for sale	0	0
Loans, net	0	0
BOLI	78,140	66,310
MSR asset	0	0
Financial liabilities:
Deposits	0	0
Long-term Debt, Fair Value	0	0
Level 2 \| Estimated Fair Value
Financial assets:
Cash and cash equivalents	0	0
Certificates of deposit in other banks	19,310	993
Securities available for sale (“AFS”), at fair value	446,172	391,654
Other investments	16,759	13,189
Loans held for sale	2,753	1,662
Loans, net	0	0
BOLI	0	0
MSR asset	0	0
Financial liabilities:
Deposits	0	0
Long-term Debt, Fair Value	25,075	34,907
Level 3 \| Estimated Fair Value
Financial assets:
Cash and cash equivalents	0	0
Certificates of deposit in other banks	0	0
Securities available for sale (“AFS”), at fair value	3,130	8,490
Other investments	3,938	2,158
Loans held for sale	0	0
Loans, net	2,593,110	2,139,322
BOLI	0	0
MSR asset	8,420	6,347
Financial liabilities:
Deposits	2,956,229	2,614,995
Long-term Debt, Fair Value	$ 41,741	$ 41,016

This element represent deposits made by entity with other banks.

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents MSR asset.

+ References

No definition available.

+ Details

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

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Investments which are not defined as or included in marketable (debt, equity, or other) securities whose use is restricted in whole or in part, generally by contractual agreements or regulatory requirements. For use in an unclassified balance sheet.

+ References

No definition available.

+ Details

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Period Type:	instant

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26610-111562

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

+ Details

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Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

No definition available.

+ Details

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- Definition

Fair value portion of the amount that could be realized under a life insurance contract or contracts owned by the entity, commonly known as corporate-owned life insurance (COLI) or bank-owned life insurance (BOLI).

+ References

No definition available.

+ Details

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- Definition

Fair value portion of deposit liabilities held by the entity, including, but not limited to, foreign and domestic, interest and noninterest bearing, demand deposits, saving deposits, negotiable orders of withdrawal (NOW) and time deposits.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

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- References

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- Definition

Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.

+ References

No definition available.

+ Details

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

- Definition

Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-URI http://asc.fasb.org/subtopic&trid=2196772

+ Details

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Balance Type:	debit
Period Type:	instant

- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

+ Details

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