SECURITIES (Securities available for sale) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 2,993,045	$ 2,492,620
Gross Unrealized Gains	42,346	4,662
Gross Unrealized Losses	(14,823)	(46,573)
Securities available for sale	3,020,568	2,450,709
Equity securities with a readily determinable fair value	18,362	17,086
Total debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,974,683	2,475,534
Gross Unrealized Gains	42,346	4,662
Gross Unrealized Losses	(14,823)	(46,573)
Securities available for sale	3,002,206	2,433,623
U.S. government corporations and agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	8,900	32,075
Gross Unrealized Gains	50	3
Gross Unrealized Losses	0	(127)
Securities available for sale	8,950	31,951
Mortgage and asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,465,561	2,061,358
Gross Unrealized Gains	28,381	3,740
Gross Unrealized Losses	(13,265)	(38,400)
Securities available for sale	2,480,677	2,026,698
Obligations of states and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	500,222	382,101
Gross Unrealized Gains	13,915	919
Gross Unrealized Losses	(1,558)	(8,046)
Securities available for sale	$ 512,579	$ 374,974

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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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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