SECURITIES (Securities available for sale) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Gross Unrealized Gains	$ 95,717	$ 29,765
Gross Unrealized Losses	(44,772)	(28,402)
Equity securities with a readily determinable fair value	19,391	18,435
Amortized, Total	4,075,406	3,311,433
Estimated Fair Value, Total	4,126,351	3,312,796
Total debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4,056,015	3,292,998
Gross Unrealized Gains	95,717	29,765
Gross Unrealized Losses	(44,772)	(28,402)
Securities available for sale	4,106,960	3,294,361
U.S. government corporations and agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5,745	9,844
Gross Unrealized Gains	97	49
Gross Unrealized Losses	0	0
Securities available for sale	5,842	9,893
Mortgage and asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	3,130,605	2,579,081
Gross Unrealized Gains	45,792	17,200
Gross Unrealized Losses	(41,958)	(19,003)
Securities available for sale	3,134,439	2,577,278
Obligations of states and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	919,665	704,073
Gross Unrealized Gains	49,828	12,516
Gross Unrealized Losses	(2,814)	(9,399)
Securities available for sale	$ 966,679	$ 707,190

Marketable Securities, Amortized Cost Basis

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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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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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Cost of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). Excludes equity method investment and investment in equity security without readily determinable fair value.

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Amount of investment in marketable security.

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