SECURITIES - Summary of Available for Sale Investment Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Available for sale:
Amortized Cost	$ 461,591	$ 639,463
Gross Unrealized Gains	6,965	4,225
Gross Unrealized Losses	(2,475)	(5,397)
Estimated Fair Value	466,081	638,291
U.S. Treasury securities
Available for sale:
Amortized Cost		50,833
Gross Unrealized Losses		(11)
Estimated Fair Value		50,822
U.S. GSE securities
Available for sale:
Amortized Cost		5,000
Gross Unrealized Losses		(5)
Estimated Fair Value		4,995
State and municipal obligations
Available for sale:
Amortized Cost	34,874	34,303
Gross Unrealized Gains	1,639	704
Gross Unrealized Losses	(9)	(43)
Estimated Fair Value	36,504	34,964
U.S. GSE residential mortgage-backed securities
Available for sale:
Amortized Cost	117,323	84,550
Gross Unrealized Gains	1,595	609
Gross Unrealized Losses	(42)	(468)
Estimated Fair Value	118,876	84,691
U.S. GSE residential collateralized mortgage obligations
Available for sale:
Amortized Cost	159,501	278,149
Gross Unrealized Gains	2,156	1,166
Gross Unrealized Losses	(75)	(1,464)
Estimated Fair Value	161,582	277,851
U.S. GSE commercial mortgage-backed securities
Available for sale:
Amortized Cost	13,179	13,656
Gross Unrealized Gains	189	23
Gross Unrealized Losses	0	(70)
Estimated Fair Value	13,368	13,609
U.S. GSE commercial collateralized mortgage obligations
Available for sale:
Amortized Cost	63,464	102,722
Gross Unrealized Gains	1,386	1,723
Gross Unrealized Losses	(58)	(289)
Estimated Fair Value	64,792	104,156
Other asset backed securities
Available for sale:
Amortized Cost	24,250	24,250
Gross Unrealized Gains	0
Gross Unrealized Losses	(356)	(849)
Estimated Fair Value	23,894	23,401
Corporate bonds
Available for sale:
Amortized Cost	49,000	46,000
Gross Unrealized Losses	(1,935)	(2,198)
Estimated Fair Value	$ 47,065	$ 43,802

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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