INVESTMENTS (Amortized Cost and Estimated Fair Values of Investments Available-for-sale) (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 730,845	$ 581,162
Gross Unrealized Gains	10,097	14,833
Gross Unrealized Losses	(7,388)	(3,946)
Estimated Fair Value	733,554	592,049
Marketable Equity Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	1,223	1,223
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	1,223	1,223
Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	729,622	579,939
Gross Unrealized Gains	10,097	14,833
Gross Unrealized Losses	(7,388)	(3,946)
Estimated Fair Value	732,331	590,826
Debt Securities \| U.S. Government Agencies
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	124,314	109,602
Gross Unrealized Gains	32	132
Gross Unrealized Losses	(2,556)	(1,334)
Estimated Fair Value	121,790	108,400
Debt Securities \| State and municipal
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	281,090	156,402
Gross Unrealized Gains	7,180	8,305
Gross Unrealized Losses	(586)	0
Estimated Fair Value	287,684	164,707
Debt Securities \| Mortgage-Backed
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	314,029	312,846
Gross Unrealized Gains	2,851	6,396
Gross Unrealized Losses	(4,169)	(2,546)
Estimated Fair Value	312,711	316,696
Debt Securities \| Trust Preferred
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	1,089	1,089
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(77)	(66)
Estimated Fair Value	1,012	1,023
Available-for-Sale Securities \| Debt Securities \| Corporate Debt
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	9,100	0
Gross Unrealized Gains	34	0
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 9,134	$ 0

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=65884222&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-Section 50
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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