LOANS HELD FOR INVESTMENT - Corporation's Nonaccrual Status and Loans 90 Days or More Still Accruing (Parenthetical) (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable Modifications [Line Items]
Financing Receivable, before Allowance for Credit Loss	$ 9,366,216	$ 9,002,205
Financing Receivable, 90 Days or More Past Due, Still Accruing	163,903	135,042
Puerto Rico and Virgin Islands regions [Member]
Financing Receivable Modifications [Line Items]
Financing Receivable, before Allowance for Credit Loss	7,356,082	7,128,277
Financing Receivable, 90 Days or More Past Due, Still Accruing	163,653	134,913
Florida region [Member]
Financing Receivable Modifications [Line Items]
Financing Receivable, before Allowance for Credit Loss	2,010,134	1,873,928
Financing Receivable, 90 Days or More Past Due, Still Accruing	250	129
Residential Portfolio Segment [Member]
Financing Receivable Modifications [Line Items]
Financing Receivable, before Allowance for Credit Loss	2,890,301	2,933,773
Residential Portfolio Segment [Member] | Puerto Rico and Virgin Islands regions [Member]
Financing Receivable Modifications [Line Items]
Financing Receivable, before Allowance for Credit Loss	2,340,289	2,367,587
Residential Portfolio Segment [Member] | Florida region [Member]
Financing Receivable Modifications [Line Items]
Financing Receivable, before Allowance for Credit Loss	550,012	566,186
Residential Portfolio Segment [Member] | GNMA [Member] | Repurchase Option Program [Member]
Financing Receivable Modifications [Line Items]
Financing Receivable, 90 Days or More Past Due, Still Accruing	69,900	35,300
Residential Portfolio Segment [Member] | GNMA [Member] | Repurchase Option Program [Member] | Puerto Rico and Virgin Islands regions [Member]
Financing Receivable Modifications [Line Items]
Financing Receivable, 90 Days or More Past Due, Still Accruing	69,900	35,300
PCD loans [Member]
Financing Receivable Modifications [Line Items]
Financing Receivable, before Allowance for Credit Loss	134,400	136,700
Financing Receivable, 90 Days or More Past Due, Still Accruing	25,300	27,000
PCD loans [Member] | Puerto Rico and Virgin Islands regions [Member]
Financing Receivable Modifications [Line Items]
Financing Receivable, before Allowance for Credit Loss	134,400	136,700
Financing Receivable, 90 Days or More Past Due, Still Accruing	25,300	27,000
Accrual Status [Member]
Financing Receivable Modifications [Line Items]
Financing Receivable, Troubled Debt Restructuring	402,700	398,300
Accrual Status [Member] | Puerto Rico and Virgin Islands regions [Member]
Financing Receivable Modifications [Line Items]
Financing Receivable, Troubled Debt Restructuring	393,100	388,400
Accrual Status [Member] | Florida region [Member]
Financing Receivable Modifications [Line Items]
Financing Receivable, Troubled Debt Restructuring	$ 9,600	$ 9,900