INVESTMENTS - Summary of Held-To-Maturity and Available-For-Sale Investment Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Investment Holdings [Line Items]
Total	$ 633,722	$ 654,008
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	2,368	5,572
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(12,123)	(6,479)
Held-to-Maturity Market Value	623,967	653,101
Total	1,370,844	1,348,227
Available for Sale Securities Gross Unrealized Gain Accumulated In Investments	5,909	8,328
Available for Sale Securities Gross Unrealized Loss Accumulated In Investments	(17,372)	(7,147)
Investment securities available-for-sale	1,359,381	1,349,408
U.S. Treasuries
Investment Holdings [Line Items]
Total	0	0
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	0	0
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	0	0
Held-to-Maturity Market Value	0	0
Total	98	98
Available for Sale Securities Gross Unrealized Gain Accumulated In Investments	0	0
Available for Sale Securities Gross Unrealized Loss Accumulated In Investments	(2)	(1)
Investment securities available-for-sale	96	97
Securities of U.S. government agencies and corporations
Investment Holdings [Line Items]
Total	10,627	11,168
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	0	0
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(188)	(76)
Held-to-Maturity Market Value	10,439	11,092
Total	25,689	15,695
Available for Sale Securities Gross Unrealized Gain Accumulated In Investments	244	220
Available for Sale Securities Gross Unrealized Loss Accumulated In Investments	(193)	0
Investment securities available-for-sale	25,740	15,915
Residential Mortgage Backed Securities [Member]
Investment Holdings [Line Items]
Total	155,208	162,093
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	1,225	2,042
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(2,817)	(1,535)
Held-to-Maturity Market Value	153,616	162,600
Total	288,757	290,793
Available for Sale Securities Gross Unrealized Gain Accumulated In Investments	375	849
Available for Sale Securities Gross Unrealized Loss Accumulated In Investments	(6,689)	(2,599)
Investment securities available-for-sale	282,443	289,043
Commercial Mortgage Backed Securities [Member]
Investment Holdings [Line Items]
Total	251,253	255,027
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	228	1,372
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(5,348)	(3,000)
Held-to-Maturity Market Value	246,133	253,399
Total	153,770	150,356
Available for Sale Securities Gross Unrealized Gain Accumulated In Investments	47	164
Available for Sale Securities Gross Unrealized Loss Accumulated In Investments	(2,875)	(1,417)
Investment securities available-for-sale	150,942	149,103
Collateralized Mortgage Backed Securities [Member]
Investment Holdings [Line Items]
Total	135,143	143,545
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	86	354
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(2,798)	(1,602)
Held-to-Maturity Market Value	132,431	142,297
Total	305,496	306,095
Available for Sale Securities Gross Unrealized Gain Accumulated In Investments	558	1,158
Available for Sale Securities Gross Unrealized Loss Accumulated In Investments	(4,791)	(1,861)
Investment securities available-for-sale	301,263	305,392
Obligations of state and other political subdivisions
Investment Holdings [Line Items]
Total	81,491	82,175
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	829	1,804
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(972)	(266)
Held-to-Maturity Market Value	81,348	83,713
Total	121,813	124,269
Available for Sale Securities Gross Unrealized Gain Accumulated In Investments	1,307	2,162
Available for Sale Securities Gross Unrealized Loss Accumulated In Investments	(1,696)	(676)
Investment securities available-for-sale	121,424	125,755
Asset-backed Securities [Member]
Investment Holdings [Line Items]
Total	0	0
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	0	0
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	0	0
Held-to-Maturity Market Value	0	0
Total	391,943	377,655
Available for Sale Securities Gross Unrealized Gain Accumulated In Investments	1,351	1,628
Available for Sale Securities Gross Unrealized Loss Accumulated In Investments	(782)	(306)
Investment securities available-for-sale	392,512	378,977
Other securities
Investment Holdings [Line Items]
Total	0	0
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	0	0
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	0	0
Held-to-Maturity Market Value	0	0
Total	83,278	83,266
Available for Sale Securities Gross Unrealized Gain Accumulated In Investments	2,027	2,147
Available for Sale Securities Gross Unrealized Loss Accumulated In Investments	(344)	(287)
Investment securities available-for-sale	$ 84,961	$ 85,126

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

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