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, 2018	Dec. 31, 2017
FHLMC [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 387,703	$ 375,719
Fair Value	379,653	370,855
GNMA [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	239,698	250,140
Fair Value	242,211	257,192
FNMA [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	791,200	801,198
Fair Value	775,673	796,726
FHLB [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	334,717	299,949
Fair Value	$ 330,714	$ 296,767