Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Basic earnings per common share computation:
Net income per consolidated statements of income	$ 5,565us-gaap_NetIncomeLoss	$ 5,166us-gaap_NetIncomeLoss
Net earnings allocated to participating securities	(29)	(22)
Net earnings allocated to common stock	5,536	5,144
Weighted average common shares outstanding, including shares considered participating securities	14,424	14,444
Less: Average participating securities	(67)ccne_AverageParticipatingSecurities	(52)ccne_AverageParticipatingSecurities
Weighted average shares	14,357	14,392
Basic earnings per common share	$ 0.39us-gaap_EarningsPerShareBasic	$ 0.36us-gaap_EarningsPerShareBasic
Diluted earnings per common share computation:
Net earnings allocated to common stock	5,536	5,144
Weighted average common shares outstanding for basic earnings per common share	14,357	14,392
Add: Dilutive effects of assumed exercises of stock options	0	2
Weighted average shares and dilutive potential common shares	14,357	14,394
Diluted earnings per common share	$ 0.39us-gaap_EarningsPerShareDiluted	$ 0.36us-gaap_EarningsPerShareDiluted
Distributed Earnings Allocated to Common Stock [Member]
Basic earnings per common share computation:
Net earnings allocated to common stock	2,370	2,375
Undistributed Earnings Allocated to Common Stock [Member]
Basic earnings per common share computation:
Net earnings allocated to common stock	$ 3,166	$ 2,769

Average participating securities.

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Net earnings allocated to participating securities.

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The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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Net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period).

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Net Income or Loss Available to Common Stockholders plus adjustments resulting from the assumption that dilutive convertible securities were converted, options or warrants were exercised, or that other shares were issued upon the satisfaction of certain conditions.

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The weighted average number of shares (units) outstanding in the calculation of pro forma basic earnings per share (earnings per unit), which is commonly presented in initial public offerings based on the terms of the offering.

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The sum of dilutive potential common shares or units used in the calculation of the diluted per-share or per-unit computation.

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

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