INVESTMENT AND MORTGAGE-BACKED SECURITIES - Amortized Cost and Fair Value By Contractual Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Available for sale, Amortized Cost
Within one year	$ 852
One to five years	281,148
Five to ten years	222,851
Beyond ten years	13,145
Pass-through MBS issued by GSEs and Agency CMO	1,056,098
Amortized Cost	1,574,094	$ 520,261
Available for sale, Fair Value
Within one year	858
One to five years	277,877
Five to ten years	224,137
Beyond ten years	13,127
Pass-through MBS issued by GSEs and Agency CMO	1,047,712
Total	1,563,711	538,861
Held-to-maturity, Amortized Cost
Pass-through MBS issued by GSEs and agency CMO	179,309
Total	179,309
Held-to-maturity, Fair Value
Pass-through MBS issued by GSEs and agency CMO	177,354
Fair Value	$ 177,354	$ 0