SECURITIES - Additional Information (Detail) - USD ($)	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016
Schedule Of Securities [Line Items]
Proceeds from sale of available-for-sale securities	$ 786,762,000	$ 615,199,000
Available-for-sale, realized gain (loss)	3,700,000
Available-for-sale securities, gross realized gains	4,700,000
Available-for-sale securities, gross realized loss	1,000,000
Proceeds from sale of held-to-maturity securities	57,050,000	0
Held-to-maturity securities, sold security, at carrying value	54,900,000
Held-to-maturity, realized gain (loss)	2,200,000
Held-to-maturity securities, realized gain	2,200,000
Held-to-maturity securities, realized loss	$ 4,000
Held-to-maturity, return on principal percentage (more than)	85.00%
OTTI losses on securities	$ 0	$ 0
Municipal bond portfolio, value	$ 839,300,000
Percentage of formal credit enhancement insurance of municipalities	62.00%
Municipal Bonds [Member] \| Weighted Average [Member]
Schedule Of Securities [Line Items]
Average holding size of securities in bond portfolio	$ 2,800,000
Municipal Bonds [Member] \| Credit Concentration Risk [Member] \| General Obligation Bonds [Member] \| A Rating [Member] \| Minimum [Member]
Schedule Of Securities [Line Items]
Percentage of portfolio	99.00%
Municipal Bonds [Member] \| Geographic Concentration Risk [Member] \| Pennsylvania, Ohio and Maryland [Member]
Schedule Of Securities [Line Items]
Percentage of portfolio	64.10%

The average holding size, aggregate value, of the securities in the municipal bond portfolio.

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Held-to-maturity Securities, Realized Gain

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Held-to-maturity Securities, Realized Loss

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Held-to-maturity Securities, Sold Security, Return On Principal Percentage

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The percentage as of the balance sheet date of municipal bonds that have formal credit enhancement insurance.

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Schedule Of Securities [Line Items]

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This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27357-111563

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This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

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This item represents the gross loss realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-SubTopic 10
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For any sales of securities categorized as held-to-maturity, this item represents the net carrying amount of the sold security.

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-Publisher FASB
-Name Accounting Standards Codification
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-Paragraph 10
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This item represents the gain (loss) realized on the sale of held-to-maturity securities disposed of during the period.

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Bonds or similar securities issued by state, city, or local governments or the agencies operated by state, city, or local governments which are 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. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

+ References

No definition available.

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The amount by which the fair value of an investment in debt and equity securities categorized as Available-for-sale is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

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The cash inflow associated with the sale of debt and equity securities classified as available-for-sale securities.

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The cash inflow associated with the sale of securities that had been designated as held-to-maturity. Excludes proceeds from maturities, prepayments and calls by the issuer.

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