Investment Securities (Details) - Investments classified by maturity date (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Investment securities available-for-sale:
Due in one year or less	$ 23,891
Due in one year or less	24,248
Due after one year through five years	32,274
Due after one year through five years	33,611
Due after five years through ten years	83,910
Due after five years through ten years	88,819
Due after ten years	53,795
Due after ten years	54,500
Total	267,047	281,461
Total	276,121cnob_SecuritiesAvailableForSaleNet
Investment securities held-to-maturity:
Due in one year or less	4,991
Due in one year or less	5,020
Due after one year through five years	9,207
Due after one year through five years	9,401
Due after five years through ten years	71,916
Due after five years through ten years	75,354
Due after ten years	135,940
Due after ten years	140,723
Total	231,720us-gaap_HeldToMaturitySecurities	224,682us-gaap_HeldToMaturitySecurities
Total	240,263	231,445
Total investment securities	498,767us-gaap_MarketableSecurities
Total investment securities	516,384
Residential Mortgage Backed Securities [Member]
Investment securities available-for-sale:
Investment Securities Available-for-Sale: Amortized Cost	57,300
Investment Securities Available-for-Sale: Fair Value	59,028
Total	57,300	58,836
Investment securities held-to-maturity:
Investment Securities Held-to-Maturity: Amoritzed Cost	5,542
Investment Securities Held-to-Maturity: Fair Value	5,555
Total	5,555	5,983
Commercial Mortgage Backed Securities [Member]
Investment securities available-for-sale:
Investment Securities Available-for-Sale: Amortized Cost	3,027
Investment Securities Available-for-Sale: Fair Value	3,082
Total	3,027	3,042
Investment securities held-to-maturity:
Investment Securities Held-to-Maturity: Amoritzed Cost	4,124
Investment Securities Held-to-Maturity: Fair Value	4,210
Total	4,210	4,316
Equity Securities [Member]
Investment securities available-for-sale:
Investment Securities Available-for-Sale: Amortized Cost	376
Investment Securities Available-for-Sale: Fair Value	320
Total	376	376
Other Securities [Member]
Investment securities available-for-sale:
Investment Securities Available-for-Sale: Amortized Cost	12,474
Investment Securities Available-for-Sale: Fair Value	12,513
Total	$ 12,474	$ 12,941

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