SECURITIES - Available for Sale Investment Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Amortized Cost, Available for sale:
Within one year	$ 5,049
One to five years	30,319
Five to ten years	86,271
Beyond ten years	575,742
Total	697,381	$ 775,903
Estimated Fair Value, Available for sale:
Within one year	5,028
One to five years	29,798
Five to ten years	82,093
Beyond ten years	563,967
Estimated Fair Value	680,886	759,916
U.S. GSE securities
Amortized Cost, Available for sale:
Within one year	0
One to five years	14,997
Five to ten years	15,000
Beyond ten years	0
Total	29,997	57,994
Estimated Fair Value, Available for sale:
Within one year	0
One to five years	14,546
Five to ten years	14,504
Beyond ten years	0
Estimated Fair Value	29,050	56,814
State and municipal obligations
Amortized Cost, Available for sale:
Within one year	5,049
One to five years	11,786
Five to ten years	20,186
Beyond ten years	3,959
Total	40,980	87,582
Estimated Fair Value, Available for sale:
Within one year	5,028
One to five years	11,744
Five to ten years	20,011
Beyond ten years	3,948
Estimated Fair Value	40,731	87,022
U.S. GSE residential mortgage-backed securities
Amortized Cost, Available for sale:
Within one year	0
One to five years	0
Beyond ten years	96,536
Total	96,536	189,705
Estimated Fair Value, Available for sale:
Within one year	0
One to five years	0
Beyond ten years	93,538
Estimated Fair Value	93,538	186,901
U.S. GSE residential collateralized mortgage obligations
Amortized Cost, Available for sale:
Within one year	0
One to five years	0
Five to ten years	5,085
Beyond ten years	357,820
Total	362,905	314,390
Estimated Fair Value, Available for sale:
Within one year	0
One to five years	0
Five to ten years	5,153
Beyond ten years	352,624
Estimated Fair Value	357,777	307,390
U.S. GSE commercial mortgage-backed securities
Amortized Cost, Available for sale:
Within one year	0
One to five years	3,536
Five to ten years	0
Beyond ten years	0
Total	3,536	6,017
Estimated Fair Value, Available for sale:
Within one year	0
One to five years	3,508
Five to ten years	0
Beyond ten years	0
Estimated Fair Value	3,508	5,979
U.S. GSE commercial collateralized mortgage obligations
Amortized Cost, Available for sale:
Within one year	0
One to five years	0
Five to ten years	0
Beyond ten years	93,177
Total	93,177	49,965
Estimated Fair Value, Available for sale:
Within one year	0
One to five years	0
Five to ten years	0
Beyond ten years	90,638
Estimated Fair Value	90,638	48,716
Other asset backed securities
Amortized Cost, Available for sale:
Within one year	0
One to five years	0
Five to ten years	0
Beyond ten years	24,250
Total	24,250	24,250
Estimated Fair Value, Available for sale:
Within one year	0
One to five years	0
Five to ten years	0
Beyond ten years	23,219
Estimated Fair Value	23,219	23,401
Corporate bonds
Amortized Cost, Available for sale:
Within one year	0
One to five years	0
Five to ten years	46,000
Beyond ten years	0
Total	46,000	46,000
Estimated Fair Value, Available for sale:
Within one year	0
One to five years	0
Five to ten years	42,425
Beyond ten years	0
Estimated Fair Value	$ 42,425	$ 43,693