SECURITIES - Summary of Available for Sale Investment Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Available for sale:
Amortized Cost	$ 718,415	$ 697,381
Gross Unrealized Gains	1,956	969
Gross Unrealized Losses	(12,920)	(17,464)
Estimated Fair Value	707,451	680,886
U.S. GSE securities
Available for sale:
Amortized Cost	39,971	29,997
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(496)	(947)
Estimated Fair Value	39,475	29,050
State and municipal obligations
Available for sale:
Amortized Cost	42,699	40,980
Gross Unrealized Gains	538	105
Gross Unrealized Losses	(72)	(354)
Estimated Fair Value	43,165	40,731
U.S. GSE residential mortgage-backed securities
Available for sale:
Amortized Cost	98,348	96,536
Gross Unrealized Gains	122	38
Gross Unrealized Losses	(1,858)	(3,036)
Estimated Fair Value	96,612	93,538
U.S. GSE residential collateralized mortgage obligations
Available for sale:
Amortized Cost	367,763	362,905
Gross Unrealized Gains	1,291	826
Gross Unrealized Losses	(4,118)	(5,954)
Estimated Fair Value	364,936	357,777
U.S. GSE commercial mortgage-backed securities
Available for sale:
Amortized Cost	7,050	3,536
Gross Unrealized Gains	5	0
Gross Unrealized Losses	0	(28)
Estimated Fair Value	7,055	3,508
U.S. GSE commercial collateralized mortgage obligations
Available for sale:
Amortized Cost	92,334	93,177
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1,931)	(2,539)
Estimated Fair Value	90,403	90,638
Other asset backed securities
Available for sale:
Amortized Cost	24,250	24,250
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1,152)	(1,031)
Estimated Fair Value	23,098	23,219
Corporate bonds
Available for sale:
Amortized Cost	46,000	46,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(3,293)	(3,575)
Estimated Fair Value	$ 42,707	$ 42,425