SECURITIES - Summary of Available for Sale Investment Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Available for sale:
Amortized Cost	$ 611,155	$ 697,381
Gross Unrealized Gains	5,350	969
Gross Unrealized Losses	(5,799)	(17,464)
Estimated Fair Value	610,706	680,886
U.S. GSE securities
Available for sale:
Amortized Cost	5,000	29,997
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(13)	(947)
Estimated Fair Value	4,987	29,050
State and municipal obligations
Available for sale:
Amortized Cost	29,587	40,980
Gross Unrealized Gains	813	105
Gross Unrealized Losses		(354)
Estimated Fair Value	30,400	40,731
U.S. GSE residential mortgage-backed securities
Available for sale:
Amortized Cost	89,104	96,536
Gross Unrealized Gains	530	38
Gross Unrealized Losses	(558)	(3,036)
Estimated Fair Value	89,076	93,538
U.S. GSE residential collateralized mortgage obligations
Available for sale:
Amortized Cost	309,146	362,905
Gross Unrealized Gains	1,688	826
Gross Unrealized Losses	(1,643)	(5,954)
Estimated Fair Value	309,191	357,777
U.S. GSE commercial mortgage-backed securities
Available for sale:
Amortized Cost	11,867	3,536
Gross Unrealized Gains	34	0
Gross Unrealized Losses	(16)	(28)
Estimated Fair Value	11,885	3,508
U.S. GSE commercial collateralized mortgage obligations
Available for sale:
Amortized Cost	96,201	93,177
Gross Unrealized Gains	2,285	0
Gross Unrealized Losses	(133)	(2,539)
Estimated Fair Value	98,353	90,638
Other asset backed securities
Available for sale:
Amortized Cost	24,250	24,250
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(788)	(1,031)
Estimated Fair Value	23,462	23,219
Corporate bonds
Available for sale:
Amortized Cost	46,000	46,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(2,648)	(3,575)
Estimated Fair Value	$ 43,352	$ 42,425