Fair Value Disclosures of Financial Assets and Liabilities - Additional Information (Detail)			9 Months Ended
Sep. 30, 2017 USD ($) secuirty	Dec. 31, 2016 USD ($)	Sep. 30, 2017 USD ($) secuirty
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	$ 810,433,000	$ 794,543,000	$ 810,433,000
Minimum discount rate on appraisals of collateral securing loan			10.00%
Maximum discount rate on appraisals of collateral securing loan			50.00%
Loan balances	55,852,000	51,600,000	$ 55,852,000
Related reserve	2,949,000	3,405,000	2,949,000
Commitments of lending operations	0	$ 0
Federal Agency MBS \| AAA-Rated
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	809,800,000		809,800,000
Visa \| Common Class B
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated value of shares	$ 44,100,000		$ 44,100,000
Penn Liberty Financial Corporation \| Quoted Prices in Active Markets for Identical Asset (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale securities, security \| secuirty	1		1

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

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Maximum amount of loss due to credit risk that, based on the gross fair value of the financial instrument, the entity would incur if parties to the financial instruments that make up the concentration failed completely to perform according to the terms of the contracts and the collateral or other security, if any, for the amount due proved to be of no value to the entity.

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Value of the investment at close of period. For schedules of investments that are categorized, the value would be aggregated by category. For investment in and advances to affiliates, if operations of any controlled companies are different in character from those of the company, group such affiliates within divisions and by type of activities.

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Available-For-Sale Securities, Securities

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Includes amounts for loans individually evaluated for impairment and purchased credit impaired loans that have become impaired since acquisition date.

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