INVESTMENT SECURITIES, Available-for-Sale Portfolio (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Available-for-Sale Portfolio [Abstract]
Amortized cost	$ 2,392,004	$ 2,952,278
Gross unrealized gains	46,203	10,339
Gross unrealized losses	1,105	26,568
Fair value	2,437,102	2,936,049
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized cost	2,392,004
Fair value	2,437,102
U.S. Treasury and Agency Securities [Member]
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized cost	1,482,739	2,036,474
Gross unrealized gains	24,122	2,190
Gross unrealized losses	214	14,911
Fair value	1,506,647	2,023,753
Obligations of State and Political Subdivisions [Member]
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized cost	442,942	453,640
Gross unrealized gains	15,159	6,563
Gross unrealized losses	11	1,049
Fair value	458,090	459,154
Government Agency Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized cost	406,329	390,234
Gross unrealized gains	6,330	1,526
Gross unrealized losses	843	9,283
Fair value	411,816	382,477
Corporate Debt Securities [Member]
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized cost	2,542	2,588
Gross unrealized gains	0	0
Gross unrealized losses	2	42
Fair value	2,540	2,546
Government Agency Collateralized Mortgage Obligations [Member]
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized cost	57,452	69,342
Gross unrealized gains	592	60
Gross unrealized losses	35	1,283
Fair value	$ 58,009	$ 68,119

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
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
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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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