Investment Securities (Details) - Unrealized gains on investment securities (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Investment securities available-for-sale:
Investment Securities Available-for-Sale, Amortized Cost	$ 267,047	$ 281,461
Investment Securities Available-for-Sale, Gross Unrealized Gains	9,578	8,596
Investment Securities Available-for-Sale, Gross Unrealized Losses	(504)	(525)
Investment Securities Available-for-Sale, Fair Value	276,121us-gaap_AvailableForSaleSecurities	289,532us-gaap_AvailableForSaleSecurities
Investment securities held-to-maturity:
Investment Securities Held-to-Maturity, Amortized Cost	231,720	224,682
Investment Securities Held-to-Maturity, Gross Unrealized Gains	8,643	6,858
Investment Securities Held-to-Maturity, Gross Unrealized Losses	(100)	(95)
Investment Securities Held-to-Maturity, Fair Value	240,263	231,445
Total, Amortized Cost	498,767	506,143
Total, Gross Unrealized Gains	18,221	15,454
Total, Gross Unrealized Losses	(604)	(620)
Total, Fair Value	516,384cnob_TotalInvestmentSecuritiesFairValue	520,977cnob_TotalInvestmentSecuritiesFairValue
Federal Agency Obligations [Member]
Investment securities available-for-sale:
Investment Securities Available-for-Sale, Amortized Cost	30,774	32,650
Investment Securities Available-for-Sale, Gross Unrealized Gains	463	217
Investment Securities Available-for-Sale, Gross Unrealized Losses	(4)	(50)
Investment Securities Available-for-Sale, Fair Value	31,233	32,817
Investment securities held-to-maturity:
Investment Securities Held-to-Maturity, Amortized Cost	35,393	27,103
Investment Securities Held-to-Maturity, Gross Unrealized Gains	586	322
Investment Securities Held-to-Maturity, Gross Unrealized Losses	(30)	(28)
Investment Securities Held-to-Maturity, Fair Value	35,949	27,397
Residential Mortgage Backed Securities [Member]
Investment securities available-for-sale:
Investment Securities Available-for-Sale, Amortized Cost	57,300	58,836
Investment Securities Available-for-Sale, Gross Unrealized Gains	1,737	1,531
Investment Securities Available-for-Sale, Gross Unrealized Losses	(9)	(11)
Investment Securities Available-for-Sale, Fair Value	59,028	60,356
Investment securities held-to-maturity:
Investment Securities Held-to-Maturity, Amortized Cost	5,542	5,955
Investment Securities Held-to-Maturity, Gross Unrealized Gains	26	28
Investment Securities Held-to-Maturity, Gross Unrealized Losses	(13)
Investment Securities Held-to-Maturity, Fair Value	5,555	5,983
Commercial Mortgage Backed Securities [Member]
Investment securities available-for-sale:
Investment Securities Available-for-Sale, Amortized Cost	3,027	3,042
Investment Securities Available-for-Sale, Gross Unrealized Gains	55	4
Investment Securities Available-for-Sale, Fair Value	3,082	3,046
Investment securities held-to-maturity:
Investment Securities Held-to-Maturity, Amortized Cost	4,124	4,266
Investment Securities Held-to-Maturity, Gross Unrealized Gains	86	50
Investment Securities Held-to-Maturity, Fair Value	4,210	4,316
US States and Political Subdivisions Debt Securities [Member]
Investment securities available-for-sale:
Investment Securities Available-for-Sale, Amortized Cost	8,197	8,201
Investment Securities Available-for-Sale, Gross Unrealized Gains	238	205
Investment Securities Available-for-Sale, Fair Value	8,435	8,406
Investment securities held-to-maturity:
Investment Securities Held-to-Maturity, Amortized Cost	119,384	120,144
Investment Securities Held-to-Maturity, Gross Unrealized Gains	4,966	4,512
Investment Securities Held-to-Maturity, Gross Unrealized Losses	(46)	(60)
Investment Securities Held-to-Maturity, Fair Value	124,304	124,596
Trust Preferred Securities [Member]
Investment securities available-for-sale:
Investment Securities Available-for-Sale, Amortized Cost	16,086	16,086
Investment Securities Available-for-Sale, Gross Unrealized Gains	648	489
Investment Securities Available-for-Sale, Gross Unrealized Losses	(278)	(269)
Investment Securities Available-for-Sale, Fair Value	16,456	16,306
Corporate Bonds and Notes [Member]
Investment securities available-for-sale:
Investment Securities Available-for-Sale, Amortized Cost	110,671	119,838
Investment Securities Available-for-Sale, Gross Unrealized Gains	6,190	5,950
Investment Securities Available-for-Sale, Gross Unrealized Losses	(22)	(11)
Investment Securities Available-for-Sale, Fair Value	116,839	125,777
Investment securities held-to-maturity:
Investment Securities Held-to-Maturity, Amortized Cost	38,962	38,950
Investment Securities Held-to-Maturity, Gross Unrealized Gains	1,472	1,026
Investment Securities Held-to-Maturity, Gross Unrealized Losses	(11)	(7)
Investment Securities Held-to-Maturity, Fair Value	40,423	39,969
Asset-backed Securities [Member]
Investment securities available-for-sale:
Investment Securities Available-for-Sale, Amortized Cost	26,045	27,393
Investment Securities Available-for-Sale, Gross Unrealized Gains	127	140
Investment Securities Available-for-Sale, Gross Unrealized Losses	(80)	(31)
Investment Securities Available-for-Sale, Fair Value	26,092	27,502
Certificates of Deposit [Member]
Investment securities available-for-sale:
Investment Securities Available-for-Sale, Amortized Cost	2,097	2,098
Investment Securities Available-for-Sale, Gross Unrealized Gains	31	27
Investment Securities Available-for-Sale, Gross Unrealized Losses	(5)	(2)
Investment Securities Available-for-Sale, Fair Value	2,123	2,123
Equity Securities [Member]
Investment securities available-for-sale:
Investment Securities Available-for-Sale, Amortized Cost	376	376
Investment Securities Available-for-Sale, Gross Unrealized Losses	(56)	(69)
Investment Securities Available-for-Sale, Fair Value	320	307
Other Securities [Member]
Investment securities available-for-sale:
Investment Securities Available-for-Sale, Amortized Cost	12,474	12,941
Investment Securities Available-for-Sale, Gross Unrealized Gains	89	33
Investment Securities Available-for-Sale, Gross Unrealized Losses	(50)	(82)
Investment Securities Available-for-Sale, Fair Value	12,513	12,892
US Treasury Securities [Member]
Investment securities held-to-maturity:
Investment Securities Held-to-Maturity, Amortized Cost	28,315	28,264
Investment Securities Held-to-Maturity, Gross Unrealized Gains	1,507	920
Investment Securities Held-to-Maturity, Fair Value	$ 29,822	$ 29,184

Available for sale securities gross unrealized gain accumulated in investments.

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Available for sale securities gross unrealized loss accumulated in investments.

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Held to maturity securities accumulated unrecognized holding gain.

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Held to maturity securities accumulated unrecognized gross holding loss.

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Total investment securities, amortized cost.

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Total investment securities, fair value.

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Total investment securities, gross unrealized gains.

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Total investment securities, gross unrealized losses.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount before other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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Fair value of investments in debt securities classified as held-to-maturity.

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