INVESTMENT SECURITIES, Available-for-Sale Portfolio (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Available-for-Sale Portfolio [Abstract]
Amortized cost	$ 2,952,278	$ 3,007,148
Gross unrealized gains	10,339	33,501
Gross unrealized losses	26,568	9,561
Fair value	2,936,049	3,031,088
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized cost	2,952,278
Fair value	2,936,049
U.S. Treasury and Agency Securities [Member]
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized cost	2,036,474	2,043,023
Gross unrealized gains	2,190	15,886
Gross unrealized losses	14,911	4,838
Fair value	2,023,753	2,054,071
Obligations of State and Political Subdivisions [Member]
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized cost	453,640	514,949
Gross unrealized gains	6,563	14,064
Gross unrealized losses	1,049	57
Fair value	459,154	528,956
Government Agency Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized cost	390,234	358,180
Gross unrealized gains	1,526	3,121
Gross unrealized losses	9,283	3,763
Fair value	382,477	357,538
Corporate Debt Securities [Member]
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized cost	2,588	2,648
Gross unrealized gains	0	0
Gross unrealized losses	42	25
Fair value	2,546	2,623
Government Agency Collateralized Mortgage Obligations [Member]
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized cost	69,342	88,097
Gross unrealized gains	60	155
Gross unrealized losses	1,283	878
Fair value	68,119	87,374
Marketable Equity Security [Member]
Marketable Equity Securities [Abstract]
Amortized cost	0	251
Gross unrealized gains	0	275
Gross unrealized losses	0	0
Fair value	$ 0	$ 526

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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

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