INVESTMENT SECURITIES - Aggregate amortized cost and market value of the securities by issuers when the aggregate amortized cost of the sucurities of such issuers exceed 10% of the Corporation's stockholders' equity (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
FHLMC [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 1,502,614	$ 509,769
Fair Value	1,520,819	513,249
GNMA [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	850,384	370,511
Fair Value	868,070	377,872
FNMA [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	1,662,145	915,704
Fair Value	$ 1,692,172	$ 924,663