SECURITIES - Available for Sale Investment Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Amortized Cost, Available for sale:
Within one year	$ 51,975
One to five years	43,373
Five to ten years	51,991
Beyond ten years	492,124
Total	639,463	$ 697,381
Estimated Fair Value, Available for sale:
Within one year	51,965
One to five years	43,123
Five to ten years	50,652
Beyond ten years	492,551
Estimated Fair Value	638,291	680,886
U.S. Treasury securities
Amortized Cost, Available for sale:
Within one year	50,833
One to five years	0
Total	50,833
Estimated Fair Value, Available for sale:
Within one year	50,822
One to five years	0
Estimated Fair Value	50,822
U.S. GSE securities
Amortized Cost, Available for sale:
Within one year	0
One to five years	5,000
Five to ten years	0
Beyond ten years	0
Total	5,000	29,997
Estimated Fair Value, Available for sale:
Within one year	0
One to five years	4,995
Five to ten years	0
Beyond ten years	0
Estimated Fair Value	4,995	29,050
State and municipal obligations
Amortized Cost, Available for sale:
Within one year	1,142
One to five years	14,620
Five to ten years	16,088
Beyond ten years	2,453
Total	34,303	40,980
Estimated Fair Value, Available for sale:
Within one year	1,143
One to five years	14,829
Five to ten years	16,540
Beyond ten years	2,452
Estimated Fair Value	34,964	40,731
U.S. GSE residential mortgage-backed securities
Amortized Cost, Available for sale:
Within one year	0
One to five years	0
Beyond ten years	84,550
Total	84,550	96,536
Estimated Fair Value, Available for sale:
Within one year	0
One to five years	0
Beyond ten years	84,691
Estimated Fair Value	84,691	93,538
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	0
Beyond ten years	278,149
Total	278,149	362,905
Estimated Fair Value, Available for sale:
Within one year	0
One to five years	0
Five to ten years	0
Beyond ten years	277,851
Estimated Fair Value	277,851	357,777
U.S. GSE commercial mortgage-backed securities
Amortized Cost, Available for sale:
Within one year	0
One to five years	8,753
Five to ten years	4,903
Beyond ten years	0
Total	13,656	3,536
Estimated Fair Value, Available for sale:
Within one year	0
One to five years	8,761
Five to ten years	4,848
Beyond ten years	0
Estimated Fair Value	13,609	3,508
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	102,722
Total	102,722	93,177
Estimated Fair Value, Available for sale:
Within one year	0
One to five years	0
Five to ten years	0
Beyond ten years	104,156
Estimated Fair Value	104,156	90,638
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	23,401
Estimated Fair Value	23,401	23,219
Corporate bonds
Amortized Cost, Available for sale:
Within one year	0
One to five years	15,000
Five to ten years	31,000
Beyond ten years	0
Total	46,000	46,000
Estimated Fair Value, Available for sale:
Within one year	0
One to five years	14,538
Five to ten years	29,264
Beyond ten years	0
Estimated Fair Value	$ 43,802	$ 42,425