LOANS HELD FOR INVESTMENT - Corporation's nonaccrual status and loans 90 days or more still accruing (Parenthetical) (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, before Allowance for Credit Loss	$ 11,140,582		$ 11,777,289
Financing Receivable, 90 Days or More Past Due, Still Accruing	148,082		145,095
Puerto Rico and Virgin Islands regions [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, before Allowance for Credit Loss	9,150,483		9,788,106
Financing Receivable, 90 Days or More Past Due, Still Accruing	147,832		144,845
Florida region [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, before Allowance for Credit Loss	1,990,099		1,989,183
Financing Receivable, 90 Days or More Past Due, Still Accruing	250		250
Residential Portfolio Segment [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, before Allowance for Credit Loss	3,095,015		3,521,954
Residential Portfolio Segment [Member] | Puerto Rico and Virgin Islands regions [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, before Allowance for Credit Loss	2,641,163		3,002,203
Residential Portfolio Segment [Member] | Florida region [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, before Allowance for Credit Loss	453,852		519,751
Residential Portfolio Segment [Member] | GNMA [Member] | Repurchase Option Program [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, 90 Days or More Past Due, Still Accruing	8,500		10,700
Financing Receivable, Purchase	400	$ 55,000
Residential Portfolio Segment [Member] | GNMA [Member] | Repurchase Option Program [Member] | Puerto Rico and Virgin Islands regions [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, 90 Days or More Past Due, Still Accruing	8,500		10,700
Financing Receivable, Purchase	400
PCD loans [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, before Allowance for Credit Loss	120,700		130,900
PCD loans [Member] | Puerto Rico and Virgin Islands regions [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, before Allowance for Credit Loss	120,700		130,900
Accrual Status [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Troubled Debt Restructuring	375,700		393,300
Accrual Status [Member] | Puerto Rico and Virgin Islands regions [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Troubled Debt Restructuring	369,900		386,700
Accrual Status [Member] | Florida region [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Troubled Debt Restructuring	$ 5,800		$ 6,600