SECURITIES - Available for Sale Securities in a Continuous Unrealized Loss Position (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Available for sale:
Less than 12 months, Estimated Fair Value	$ 272,887	$ 236,848
Less than 12 months, Gross Unrealized Losses	(4,677)	(2,666)
Greater than 12 months, Estimated Fair Value	384,324	481,253
Greater than 12 months, Gross Unrealized Losses	(20,571)	(13,627)
U.S. GSE securities
Available for sale:
Less than 12 months, Estimated Fair Value	0	0
Less than 12 months, Gross Unrealized Losses	0	0
Greater than 12 months, Estimated Fair Value	28,544	56,815
Greater than 12 months, Gross Unrealized Losses	(1,453)	(1,180)
State and municipal obligations
Available for sale:
Less than 12 months, Estimated Fair Value	16,037	35,350
Less than 12 months, Gross Unrealized Losses	(190)	(301)
Greater than 12 months, Estimated Fair Value	15,948	28,165
Greater than 12 months, Gross Unrealized Losses	(450)	(518)
U.S. GSE residential mortgage-backed securities
Available for sale:
Less than 12 months, Estimated Fair Value	14,098	107,408
Less than 12 months, Gross Unrealized Losses	(640)	(1,153)
Greater than 12 months, Estimated Fair Value	77,169	69,571
Greater than 12 months, Gross Unrealized Losses	(3,602)	(1,680)
U.S. GSE residential collateralized mortgage obligations
Available for sale:
Less than 12 months, Estimated Fair Value	192,703	77,705
Less than 12 months, Gross Unrealized Losses	(2,953)	(759)
Greater than 12 months, Estimated Fair Value	152,607	224,932
Greater than 12 months, Gross Unrealized Losses	(8,382)	(6,257)
U.S. GSE commercial mortgage-backed securities
Available for sale:
Less than 12 months, Estimated Fair Value	3,480	2,345
Less than 12 months, Gross Unrealized Losses	(80)	(40)
Greater than 12 months, Estimated Fair Value	0	0
Greater than 12 months, Gross Unrealized Losses	0	0
U.S. GSE commercial collateralized mortgage obligations
Available for sale:
Less than 12 months, Estimated Fair Value	46,569	452
Less than 12 months, Gross Unrealized Losses	(814)	(1)
Greater than 12 months, Estimated Fair Value	44,099	48,264
Greater than 12 months, Gross Unrealized Losses	(2,392)	(1,248)
Other asset backed securities
Available for sale:
Less than 12 months, Estimated Fair Value	0	0
Less than 12 months, Gross Unrealized Losses	0	0
Greater than 12 months, Estimated Fair Value	23,522	23,401
Greater than 12 months, Gross Unrealized Losses	(728)	(849)
Corporate bonds
Available for sale:
Less than 12 months, Estimated Fair Value		13,588
Less than 12 months, Gross Unrealized Losses		(412)
Greater than 12 months, Estimated Fair Value	42,435	30,105
Greater than 12 months, Gross Unrealized Losses	$ (3,564)	$ (1,895)