SECURITIES - Summary of Available for Sale Investment Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Available for sale:
Amortized Cost	$ 687,065	$ 775,903
Gross Unrealized Gains	45	306
Gross Unrealized Losses	(25,248)	(16,293)
Estimated Fair Value	661,862	759,916
U.S. GSE securities
Available for sale:
Amortized Cost	29,997	57,994
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1,453)	(1,180)
Estimated Fair Value	28,544	56,814
State and municipal obligations
Available for sale:
Amortized Cost	35,772	87,582
Gross Unrealized Gains	40	259
Gross Unrealized Losses	(640)	(819)
Estimated Fair Value	35,172	87,022
U.S. GSE residential mortgage-backed securities
Available for sale:
Amortized Cost	96,967	189,705
Gross Unrealized Gains	5	29
Gross Unrealized Losses	(4,242)	(2,833)
Estimated Fair Value	92,730	186,901
U.S. GSE residential collateralized mortgage obligations
Available for sale:
Amortized Cost	356,644	314,390
Gross Unrealized Gains	0	16
Gross Unrealized Losses	(11,335)	(7,016)
Estimated Fair Value	345,309	307,390
U.S. GSE commercial mortgage-backed securities
Available for sale:
Amortized Cost	3,560	6,017
Gross Unrealized Gains	0	2
Gross Unrealized Losses	(80)	(40)
Estimated Fair Value	3,480	5,979
U.S. GSE commercial collateralized mortgage obligations
Available for sale:
Amortized Cost	93,875	49,965
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(3,206)	(1,249)
Estimated Fair Value	90,669	48,716
Other asset backed securities
Available for sale:
Amortized Cost	24,250	24,250
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(728)	(849)
Estimated Fair Value	23,522	23,401
Corporate bonds
Available for sale:
Amortized Cost	46,000	46,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(3,564)	(2,307)
Estimated Fair Value	$ 42,436	$ 43,693

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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Amount 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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