SECURITIES - Summary of Available for Sale Investment Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Available for sale:
Amortized Cost	$ 697,381	$ 775,903
Gross Unrealized Gains	969	306
Gross Unrealized Losses	(17,464)	(16,293)
Estimated Fair Value	680,886	759,916
U.S. GSE securities
Available for sale:
Amortized Cost	29,997	57,994
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(947)	(1,180)
Estimated Fair Value	29,050	56,814
State and municipal obligations
Available for sale:
Amortized Cost	40,980	87,582
Gross Unrealized Gains	105	259
Gross Unrealized Losses	(354)	(819)
Estimated Fair Value	40,731	87,022
U.S. GSE residential mortgage-backed securities
Available for sale:
Amortized Cost	96,536	189,705
Gross Unrealized Gains	38	29
Gross Unrealized Losses	(3,036)	(2,833)
Estimated Fair Value	93,538	186,901
U.S. GSE residential collateralized mortgage obligations
Available for sale:
Amortized Cost	362,905	314,390
Gross Unrealized Gains	826	16
Gross Unrealized Losses	(5,954)	(7,016)
Estimated Fair Value	357,777	307,390
U.S. GSE commercial mortgage-backed securities
Available for sale:
Amortized Cost	3,536	6,017
Gross Unrealized Gains	0	2
Gross Unrealized Losses	(28)	(40)
Estimated Fair Value	3,508	5,979
U.S. GSE commercial collateralized mortgage obligations
Available for sale:
Amortized Cost	93,177	49,965
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(2,539)	(1,249)
Estimated Fair Value	90,638	48,716
Other asset backed securities
Available for sale:
Amortized Cost	24,250	24,250
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1,031)	(849)
Estimated Fair Value	23,219	23,401
Corporate bonds
Available for sale:
Amortized Cost	46,000	46,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(3,575)	(2,307)
Estimated Fair Value	$ 42,425	$ 43,693