INVESTMENTS (Summary of Amortized Costs and Estimated Fair Values of Available-For-Sale Securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
AFS Investments (carried at fair value):
Available-for-sale securities, at fair value (book value of $933,135 and $933,399, respectively)	$ 924,311	$ 910,692
HTM Investments (carried at amortized cost):
Amortized Cost	1,306	1,307
Unrealized Gains	21	8
Unrealized Losses	(3)	(24)
Fair Value	1,324	1,291
Obligations of states and political subdivisions
AFS Investments (carried at fair value):
Amortized Cost	92,030	94,430
Unrealized Gains	1,095	216
Unrealized Losses	(105)	(894)
Available-for-sale securities, at fair value (book value of $933,135 and $933,399, respectively)	93,020	93,752
HTM Investments (carried at amortized cost):
Amortized Cost	1,306	1,307
Unrealized Gains	21	8
Unrealized Losses	(3)	(24)
Fair Value	1,324	1,291
Mortgage-backed securities issued or guaranteed by U.S. government-sponsored enterprises
AFS Investments (carried at fair value):
Amortized Cost	453,980	466,613
Unrealized Gains	1,290	583
Unrealized Losses	(6,449)	(13,524)
Available-for-sale securities, at fair value (book value of $933,135 and $933,399, respectively)	448,821	453,672
Collateralized mortgage obligations issued or guaranteed by U.S. government-sponsored enterprises
AFS Investments (carried at fair value):
Amortized Cost	366,727	351,958
Unrealized Gains	1,888	1,007
Unrealized Losses	(7,215)	(10,071)
Available-for-sale securities, at fair value (book value of $933,135 and $933,399, respectively)	361,400	342,894
Subordinated corporate bonds
AFS Investments (carried at fair value):
Amortized Cost	20,398	20,398
Unrealized Gains	672	23
Unrealized Losses	0	(47)
Available-for-sale securities, at fair value (book value of $933,135 and $933,399, respectively)	21,070	20,374
Total AFS investments
AFS Investments (carried at fair value):
Amortized Cost	933,135	933,399
Unrealized Gains	4,945	1,829
Unrealized Losses	(13,769)	(24,536)
Available-for-sale securities, at fair value (book value of $933,135 and $933,399, respectively)	$ 924,311	$ 910,692

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

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-Publisher FASB
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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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