Fair value of financial instruments - Carrying or notional amounts and estimated fair values for financial instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024	Mar. 31, 2024	Dec. 31, 2023
Financial Assets:
Cash and due from banks	$ 380,165	$ 419,638
Money market investments	6,195,028	6,380,948
Debt securities available-for-sale	19,493,180	18,245,903
Debt securities held-to-maturity	7,643,237	7,752,760
Equity securities:
Equity securities, at lower of cost or realizable value	205,021	208,166
Loans held in portfolio	36,491,884	36,361,628
Mortgage servicing rights	104,743	108,103	$ 114,964	$ 118,109
Deposits
Time deposits	9,168,137	9,012,882
Deposits	65,819,255	64,884,345
Assets sold under agreements to repurchase	57,268	54,833
Other short-term borrowings	200,000	225,000
Notes payable:
Notes payable	833,149	896,293
US Treasury Securities
Financial Assets:
Debt securities available-for-sale	14,273,968	12,995,110
Debt securities held-to-maturity	7,586,169	7,693,418
Obligations of Puerto Rico, States and political subdivisions
Financial Assets:
Debt securities held-to-maturity	49,594	51,865
Collateralized Mortgage Obligations - Federal agencies
Financial Assets:
Debt securities available-for-sale	115,859	120,284
Debt securities held-to-maturity	1,514	1,518
Securities in wholly owned statutory business trusts
Financial Assets:
Debt securities held-to-maturity	5,960	5,959
Other
Financial Assets:
Debt securities available-for-sale	750	2,250
Carrying amount
Financial Assets:
Cash and due from banks	380,165	419,638
Money market investments	6,195,028	6,380,948
Trading account debt securities, excluding derivatives	28,477	32,783
Debt securities available-for-sale	19,493,180	18,245,903
Debt securities held-to-maturity	7,643,237	7,752,760
Equity securities:
FHLB stock	51,428	55,786
FRB stock	100,526	100,304
Other investments	53,067	52,076
Equity securities, at lower of cost or realizable value	205,021	208,166
Loans held-for-sale	5,077	5,423
Loans held in portfolio	36,491,884	36,361,628
Mortgage servicing rights	104,743	108,103
Derivatives	20,828	26,023
Deposits
Demand deposits	56,651,118	55,871,463
Time deposits	9,168,137	9,012,882
Deposits	65,819,255	64,884,345
Assets sold under agreements to repurchase	57,268	54,833
Other short-term borrowings	200,000	225,000
Notes payable:
FHLB advances	239,199	302,722
Unsecured senior debt securities	395,570	395,198
Junior subordinated deferrable interest debentures (related to trust preferred securities)	198,380	198,373
Notes payable	833,149	896,293
Derivatives	19,523	22,832
Carrying amount | US Treasury Securities
Financial Assets:
Debt securities held-to-maturity	7,586,169	7,693,418
Carrying amount | Obligations of Puerto Rico, States and political subdivisions
Financial Assets:
Debt securities held-to-maturity	49,594	51,865
Carrying amount | Collateralized Mortgage Obligations - Federal agencies
Financial Assets:
Debt securities held-to-maturity	1,514	1,518
Carrying amount | Securities in wholly owned statutory business trusts
Financial Assets:
Debt securities held-to-maturity	5,960	5,959
Fair Value
Financial Assets:
Cash and due from banks	380,165	419,638
Money market investments	6,195,028	6,380,948
Trading account debt securities, excluding derivatives	28,477	32,783
Debt securities available-for-sale	19,493,180	18,245,903
Debt securities held-to-maturity	7,640,686	7,682,664
Equity securities:
FHLB stock	51,428	55,786
FRB stock	100,526	100,304
Other investments	53,561	52,573
Equity securities, at lower of cost or realizable value	205,515	208,663
Loans held-for-sale	5,077	5,423
Loans held in portfolio	35,777,886	35,652,539
Mortgage servicing rights	104,743	108,103
Derivatives	20,828	26,023
Deposits
Demand deposits	56,651,118	55,871,463
Time deposits	8,929,129	8,795,803
Deposits	65,580,247	64,667,266
Assets sold under agreements to repurchase	57,274	54,845
Other short-term borrowings	200,000	225,000
Notes payable:
FHLB advances	234,299	295,023
Unsecured senior debt securities	415,132	415,148
Junior subordinated deferrable interest debentures (related to trust preferred securities)	189,227	189,758
Notes payable	838,658	899,929
Derivatives	19,523	22,832
Fair Value | US Treasury Securities
Financial Assets:
Debt securities held-to-maturity	7,583,514	7,623,824
Fair Value | Obligations of Puerto Rico, States and political subdivisions
Financial Assets:
Debt securities held-to-maturity	49,883	51,577
Fair Value | Collateralized Mortgage Obligations - Federal agencies
Financial Assets:
Debt securities held-to-maturity	1,329	1,304
Fair Value | Securities in wholly owned statutory business trusts
Financial Assets:
Debt securities held-to-maturity	5,960	5,959
Fair Value | Level 1
Financial Assets:
Cash and due from banks	380,165	419,638
Money market investments	6,184,571	6,371,180
Trading account debt securities, excluding derivatives	8,524	2,814
Debt securities available-for-sale	8,601,447	7,512,171
Debt securities held-to-maturity	0	0
Equity securities:
FHLB stock	0	0
FRB stock	0	0
Other investments	0	0
Equity securities, at lower of cost or realizable value	0	0
Loans held-for-sale	0	0
Loans held in portfolio	0	0
Mortgage servicing rights	0	0
Derivatives	0	0
Deposits
Demand deposits	0	0
Time deposits	0	0
Deposits	0	0
Assets sold under agreements to repurchase	0	0
Other short-term borrowings	0	0
Notes payable:
FHLB advances	0	0
Unsecured senior debt securities	0	0
Junior subordinated deferrable interest debentures (related to trust preferred securities)	0	0
Notes payable	0	0
Derivatives	0	0
Fair Value | Level 1 | US Treasury Securities
Financial Assets:
Debt securities held-to-maturity	0	0
Fair Value | Level 1 | Obligations of Puerto Rico, States and political subdivisions
Financial Assets:
Debt securities held-to-maturity	0	0
Fair Value | Level 1 | Collateralized Mortgage Obligations - Federal agencies
Financial Assets:
Debt securities held-to-maturity	0	0
Fair Value | Level 1 | Securities in wholly owned statutory business trusts
Financial Assets:
Debt securities held-to-maturity	0	0
Fair Value | Level 2
Financial Assets:
Cash and due from banks	0	0
Money market investments	10,457	9,768
Trading account debt securities, excluding derivatives	19,742	29,752
Debt securities available-for-sale	10,890,526	10,730,998
Debt securities held-to-maturity	7,597,656	7,637,953
Equity securities:
FHLB stock	51,428	55,786
FRB stock	100,526	100,304
Other investments	45,129	45,664
Equity securities, at lower of cost or realizable value	197,083	201,754
Loans held-for-sale	5,077	5,423
Loans held in portfolio	0	0
Mortgage servicing rights	0	0
Derivatives	20,828	26,023
Deposits
Demand deposits	56,651,118	55,871,463
Time deposits	8,929,129	8,795,803
Deposits	65,580,247	64,667,266
Assets sold under agreements to repurchase	57,274	54,845
Other short-term borrowings	200,000	225,000
Notes payable:
FHLB advances	234,299	295,023
Unsecured senior debt securities	415,132	415,148
Junior subordinated deferrable interest debentures (related to trust preferred securities)	189,227	189,758
Notes payable	838,658	899,929
Derivatives	19,523	22,832
Fair Value | Level 2 | US Treasury Securities
Financial Assets:
Debt securities held-to-maturity	7,583,514	7,623,824
Fair Value | Level 2 | Obligations of Puerto Rico, States and political subdivisions
Financial Assets:
Debt securities held-to-maturity	6,853	6,866
Fair Value | Level 2 | Collateralized Mortgage Obligations - Federal agencies
Financial Assets:
Debt securities held-to-maturity	1,329	1,304
Fair Value | Level 2 | Securities in wholly owned statutory business trusts
Financial Assets:
Debt securities held-to-maturity	5,960	5,959
Fair Value | Level 3
Financial Assets:
Cash and due from banks	0	0
Money market investments	0	0
Trading account debt securities, excluding derivatives	211	217
Debt securities available-for-sale	1,207	2,734
Debt securities held-to-maturity	43,030	44,711
Equity securities:
FHLB stock	0	0
FRB stock	0	0
Other investments	8,025	6,528
Equity securities, at lower of cost or realizable value	8,025	6,528
Loans held-for-sale	0	0
Loans held in portfolio	35,777,886	35,652,539
Mortgage servicing rights	104,743	108,103
Derivatives	0	0
Deposits
Demand deposits	0	0
Time deposits	0	0
Deposits	0	0
Assets sold under agreements to repurchase	0	0
Other short-term borrowings	0	0
Notes payable:
FHLB advances	0	0
Unsecured senior debt securities	0	0
Junior subordinated deferrable interest debentures (related to trust preferred securities)	0	0
Notes payable	0	0
Derivatives	0	0
Fair Value | Level 3 | US Treasury Securities
Financial Assets:
Debt securities held-to-maturity	0	0
Fair Value | Level 3 | Obligations of Puerto Rico, States and political subdivisions
Financial Assets:
Debt securities held-to-maturity	43,030	44,711
Fair Value | Level 3 | Collateralized Mortgage Obligations - Federal agencies
Financial Assets:
Debt securities held-to-maturity	0	0
Fair Value | Level 3 | Securities in wholly owned statutory business trusts
Financial Assets:
Debt securities held-to-maturity	0	0
Fair Value | NAV
Financial Assets:
Cash and due from banks	0	0
Money market investments	0	0
Trading account debt securities, excluding derivatives	0	0
Debt securities available-for-sale	0	0
Debt securities held-to-maturity	0	0
Equity securities:
FHLB stock	0	0
FRB stock	0	0
Other investments	407	381
Equity securities, at lower of cost or realizable value	407	381
Loans held-for-sale	0	0
Loans held in portfolio	0	0
Mortgage servicing rights	0	0
Derivatives	0	0
Deposits
Demand deposits	0	0
Time deposits	0	0
Deposits	0	0
Assets sold under agreements to repurchase	0	0
Other short-term borrowings	0	0
Notes payable:
FHLB advances	0	0
Unsecured senior debt securities	0	0
Junior subordinated deferrable interest debentures (related to trust preferred securities)	0	0
Notes payable	0	0
Derivatives	0	0
Fair Value | NAV | US Treasury Securities
Financial Assets:
Debt securities held-to-maturity	0	0
Fair Value | NAV | Obligations of Puerto Rico, States and political subdivisions
Financial Assets:
Debt securities held-to-maturity	0	0
Fair Value | NAV | Collateralized Mortgage Obligations - Federal agencies
Financial Assets:
Debt securities held-to-maturity	0	0
Fair Value | NAV | Securities in wholly owned statutory business trusts
Financial Assets:
Debt securities held-to-maturity	$ 0	$ 0