SECURITIES - Summary of Held to Maturity Investment Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Held to maturity:
Amortized Cost	$ 164,438	$ 180,866
Gross Unrealized Gains	349	1,293
Gross Unrealized Losses	(5,543)	(2,274)
Estimated Fair Value	159,244	179,885
State and municipal obligations
Held to maturity:
Amortized Cost	55,828	60,762
Gross Unrealized Gains	327	972
Gross Unrealized Losses	(664)	(64)
Estimated Fair Value	55,491	61,670
U.S. GSE residential mortgage-backed securities
Held to maturity:
Amortized Cost	10,042	11,424
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(481)	(261)
Estimated Fair Value	9,561	11,163
U.S. GSE residential collateralized mortgage obligations
Held to maturity:
Amortized Cost	49,470	54,250
Gross Unrealized Gains	22	244
Gross Unrealized Losses	(1,766)	(666)
Estimated Fair Value	47,726	53,828
U.S. GSE commercial mortgage-backed securities
Held to maturity:
Amortized Cost	19,285	22,953
Gross Unrealized Gains	0	77
Gross Unrealized Losses	(973)	(438)
Estimated Fair Value	18,312	22,592
U.S. GSE commercial collateralized mortgage obligations
Held to maturity:
Amortized Cost	29,813	31,477
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1,659)	(845)
Estimated Fair Value	$ 28,154	$ 30,632

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

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

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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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