INVESTMENT SECURITIES - Aggregate amortized cost and market value of the securities by issuers (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule Of Available-For-Sale And Held-To-Maturity Securities [Line Items]
Amortized cost	$ 1,908,557	$ 1,906,391
Fair Value	1,881,920	1,886,395
Federal Home Loan Mortgage Corporation Certificates And Obligations F H L M C [Member]
Schedule Of Available-For-Sale And Held-To-Maturity Securities [Line Items]
Amortized cost	399,955	323,437
Fair Value	394,249	322,772
Government National Mortgage Association Certificates And Obligations G N M A [Member]
Schedule Of Available-For-Sale And Held-To-Maturity Securities [Line Items]
Amortized cost	254,495	285,584
Fair Value	265,615	301,573
Federal National Mortgage Association Certificates And Obligations F N M A [Member]
Schedule Of Available-For-Sale And Held-To-Maturity Securities [Line Items]
Amortized cost	849,584	954,178
Fair Value	843,818	953,866
FHLB [Member]
Schedule Of Available-For-Sale And Held-To-Maturity Securities [Line Items]
Amortized cost	231,666	223,049
Fair Value	$ 229,792	$ 219,320