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INVESTMENT SECURITIES, Available-for-Sale Portfolio (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Available-for-Sale Portfolio [Abstract]
Amortized cost	$ 2,915,267	$ 2,952,278
Gross unrealized gains	18,835	10,339
Gross unrealized losses	11,159	26,568
Fair value	2,922,943	2,936,049
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized cost	2,915,267
Fair value	2,922,943
U.S. Treasury and Agency Securities [Member]
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized cost	2,033,399	2,036,474
Gross unrealized gains	6,841	2,190
Gross unrealized losses	5,268	14,911
Fair value	2,034,972	2,023,753
Obligations of State and Political Subdivisions [Member]
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized cost	423,916	453,640
Gross unrealized gains	9,319	6,563
Gross unrealized losses	76	1,049
Fair value	433,159	459,154
Government Agency Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized cost	389,154	390,234
Gross unrealized gains	2,587	1,526
Gross unrealized losses	5,198	9,283
Fair value	386,543	382,477
Corporate Debt Securities [Member]
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized cost	2,572	2,588
Gross unrealized gains	0	0
Gross unrealized losses	19	42
Fair value	2,553	2,546
Government Agency Collateralized Mortgage Obligations [Member]
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized cost	66,226	69,342
Gross unrealized gains	88	60
Gross unrealized losses	598	1,283
Fair value	$ 65,716	$ 68,119

X

- Definition

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).

+ References

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-Publisher FASB
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-Topic 320
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-Section 50
-Paragraph 2
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