INVESTMENTS (Summary of Amortized Costs and Estimated Fair Values of Available-For-Sale Securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Investments [Line Items]
Available-for-sale securities, at fair value	$ 796,687	$ 789,899
Held-to-maturity securities, at amortized cost	93,192	94,073
Held-to-maturity securities, Unrealized Gains	130	1,077
Held-to-maturity securities, Unrealized Losses	(1,448)	(237)
Held-to-maturity Securities, Fair Value	91,874	94,913
Obligations of states and political subdivisions
Schedule of Investments [Line Items]
Available-for-sale, Amortized Cost	5,776	7,232
Available-for-sale, Unrealized Gains	55	103
Available-for-sale, Unrealized Losses	(4)	0
Available-for-sale securities, at fair value	5,827	7,335
Held-to-maturity securities, at amortized cost	93,192	94,073
Held-to-maturity securities, Unrealized Gains	130	1,077
Held-to-maturity securities, Unrealized Losses	(1,448)	(237)
Held-to-maturity Securities, Fair Value	91,874	94,913
Mortgage-backed securities issued or guaranteed by U.S. government-sponsored enterprises
Schedule of Investments [Line Items]
Available-for-sale, Amortized Cost	517,823	510,176
Available-for-sale, Unrealized Gains	490	597
Available-for-sale, Unrealized Losses	(15,317)	(7,471)
Available-for-sale securities, at fair value	502,996	503,302
Collateralized mortgage obligations issued or guaranteed by U.S. government-sponsored enterprises
Schedule of Investments [Line Items]
Available-for-sale, Amortized Cost	293,371	279,575
Available-for-sale, Unrealized Gains	6	14
Available-for-sale, Unrealized Losses	(11,098)	(6,790)
Available-for-sale securities, at fair value	282,279	272,799
Corporate Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale, Amortized Cost	5,485	5,484
Available-for-sale, Unrealized Gains	119	173
Available-for-sale, Unrealized Losses	(19)	0
Available-for-sale securities, at fair value	5,585	5,657
Equity Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale, Amortized Cost		554
Available-for-sale, Unrealized Gains		252
Available-for-sale, Unrealized Losses		0
Available-for-sale securities, at fair value		806
Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale, Amortized Cost	822,455	803,021
Available-for-sale, Unrealized Gains	670	1,139
Available-for-sale, Unrealized Losses	(26,438)	(14,261)
Available-for-sale securities, at fair value	$ 796,687	$ 789,899

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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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 after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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