INVESTMENTS - Summary of Held-To-Maturity and Available-For-Sale Investment Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Investment Holdings [Line Items]
Total	$ 154,327	$ 429,328
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	1,007	2,212
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	(2,295)	(7,422)
Held-to-Maturity Market Value	153,039	424,118
Total	3,104,152	2,792,326
Available for Sale Securities Gross Unrealized Gain Accumulated In Investments	54,060	9,409
Available for Sale Securities Gross Unrealized Loss Accumulated In Investments	(5,242)	(22,480)
Investment securities available-for-sale	3,152,970	2,779,255
U.S. Treasuries
Investment Holdings [Line Items]
Total	0	0
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	0	0
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	0	0
Held-to-Maturity Market Value	0	0
Total	99	99
Available for Sale Securities Gross Unrealized Gain Accumulated In Investments	1	0
Available for Sale Securities Gross Unrealized Loss Accumulated In Investments	0	(2)
Investment securities available-for-sale	100	97
Securities of U.S. government agencies and corporations
Investment Holdings [Line Items]
Total	0	0
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	0	0
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	0	0
Held-to-Maturity Market Value	0	0
Total	24,709	32,095
Available for Sale Securities Gross Unrealized Gain Accumulated In Investments	239	57
Available for Sale Securities Gross Unrealized Loss Accumulated In Investments	(139)	(233)
Investment securities available-for-sale	24,809	31,919
Residential Mortgage Backed Securities [Member]
Investment Holdings [Line Items]
Total	23,736	25,565
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	163	0
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	(194)	(1,045)
Held-to-Maturity Market Value	23,705	24,520
Total	507,434	565,071
Available for Sale Securities Gross Unrealized Gain Accumulated In Investments	7,716	691
Available for Sale Securities Gross Unrealized Loss Accumulated In Investments	(1,161)	(7,163)
Investment securities available-for-sale	513,989	558,599
Commercial Mortgage Backed Securities [Member]
Investment Holdings [Line Items]
Total	107,810	147,780
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	248	258
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	(1,809)	(4,385)
Held-to-Maturity Market Value	106,249	143,653
Total	482,157	423,797
Available for Sale Securities Gross Unrealized Gain Accumulated In Investments	5,815	819
Available for Sale Securities Gross Unrealized Loss Accumulated In Investments	(1,327)	(3,581)
Investment securities available-for-sale	486,645	421,035
Collateralized Mortgage Backed Securities [Member]
Investment Holdings [Line Items]
Total	11,264	12,540
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	0	0
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	(181)	(633)
Held-to-Maturity Market Value	11,083	11,907
Total	940,304	928,586
Available for Sale Securities Gross Unrealized Gain Accumulated In Investments	18,613	4,319
Available for Sale Securities Gross Unrealized Loss Accumulated In Investments	(531)	(6,158)
Investment securities available-for-sale	958,386	926,747
Obligations of state and other political subdivisions
Investment Holdings [Line Items]
Total	11,517	243,443
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	596	1,954
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	(111)	(1,359)
Held-to-Maturity Market Value	12,002	244,038
Total	549,546	257,300
Available for Sale Securities Gross Unrealized Gain Accumulated In Investments	18,991	2,554
Available for Sale Securities Gross Unrealized Loss Accumulated In Investments	(110)	(1,429)
Investment securities available-for-sale	568,427	258,425
Asset-backed Securities [Member]
Investment Holdings [Line Items]
Total	0	0
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	0	0
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	0	0
Held-to-Maturity Market Value	0	0
Total	521,357	511,430
Available for Sale Securities Gross Unrealized Gain Accumulated In Investments	1,349	611
Available for Sale Securities Gross Unrealized Loss Accumulated In Investments	(1,605)	(2,810)
Investment securities available-for-sale	521,101	509,231
Other securities
Investment Holdings [Line Items]
Total	0	0
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	0	0
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	0	0
Held-to-Maturity Market Value	0	0
Total	78,546	73,948
Available for Sale Securities Gross Unrealized Gain Accumulated In Investments	1,336	358
Available for Sale Securities Gross Unrealized Loss Accumulated In Investments	(369)	(1,104)
Investment securities available-for-sale	$ 79,513	$ 73,202

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount of accumulated unrecognized gain on investment in debt security measured at amortized cost (held-to-maturity).

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