Fair value of financial instruments - Carrying or notional amounts and estimated fair values for financial instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022	Dec. 31, 2021
Financial Assets:
Cash and due from banks	$ 462,013	$ 469,501
Money market investments	6,098,288	5,614,595
Debt securities available-for-sale	17,173,128	17,804,374
Debt securities held-to-maturity	8,556,260	8,518,455
Equity securities:
Equity securities, at lower of cost or realizable value	185,917	195,854
Loans held in portfolio	31,649,253	31,357,467
Mortgage servicing rights	127,475	128,350	$ 125,358	$ 121,570
Deposits
Time deposits	7,406,126	6,781,401
Deposits	60,953,888	61,227,227
Assets sold under agreements to repurchase	123,499	148,609
Other short-term borrowings	0	365,000
Notes payable:
Notes payable	1,279,127	886,710
US Treasury Securities
Financial Assets:
Debt securities available-for-sale	10,634,747	11,180,948
Debt securities held-to-maturity	8,494,652	8,453,467
Obligations of Puerto Rico, States and political subdivisions
Financial Assets:
Debt securities held-to-maturity	55,633	59,010
Collateralized Mortgage Obligations - Federal agencies
Financial Assets:
Debt securities available-for-sale	158,772	165,196
Debt securities held-to-maturity	16	19
Securities in wholly owned statutory business trusts
Financial Assets:
Debt securities held-to-maturity	5,959	5,959
Other
Financial Assets:
Debt securities available-for-sale	1,049	1,060
Carrying amount
Financial Assets:
Cash and due from banks	462,013	469,501
Money market investments	6,098,288	5,614,595
Trading account debt securities, excluding derivatives	29,823	27,723
Debt securities available-for-sale	17,173,128	17,804,374
Debt securities held-to-maturity	8,556,260	8,518,455
Equity securities:
FHLB stock	49,265	65,861
FRB stock	99,134	96,206
Other investments	37,518	33,787
Equity securities, at lower of cost or realizable value	185,917	195,854
Loans held-for-sale	11,181	5,381
Loans held in portfolio	31,649,253	31,357,467
Mortgage servicing rights	127,475	128,350
Derivatives	19,365	19,229
Deposits
Demand deposits	53,547,761	54,445,825
Time deposits	7,406,127	6,781,402
Deposits	60,953,888	61,227,227
Assets sold under agreements to repurchase	123,499	148,609
Other short-term borrowings	0	365,000
Notes payable:
FHLB advances	388,282	389,282
Unsecured senior debt securities	692,519	299,109
Junior subordinated deferrable interest debentures (related to trust preferred securities)	198,326	198,319
Notes payable	1,279,127	886,710
Derivatives	17,115	17,000
Carrying amount | US Treasury Securities
Financial Assets:
Debt securities held-to-maturity	8,494,652	8,453,467
Carrying amount | Obligations of Puerto Rico, States and political subdivisions
Financial Assets:
Debt securities held-to-maturity	55,633	59,010
Carrying amount | Collateralized Mortgage Obligations - Federal agencies
Financial Assets:
Debt securities held-to-maturity	16	19
Carrying amount | Securities in wholly owned statutory business trusts
Financial Assets:
Debt securities held-to-maturity	5,959	5,959
Fair Value
Financial Assets:
Cash and due from banks	462,013	469,501
Money market investments	6,098,288	5,614,595
Trading account debt securities, excluding derivatives	29,823	27,723
Debt securities available-for-sale	17,173,128	17,804,374
Debt securities held-to-maturity	8,597,919	8,440,196
Equity securities:
FHLB stock	49,265	65,861
FRB stock	99,134	96,206
Other investments	38,345	34,598
Equity securities, at lower of cost or realizable value	186,744	196,665
Loans held-for-sale	11,181	5,404
Loans held in portfolio	30,066,069	29,366,365
Mortgage servicing rights	127,475	128,350
Derivatives	19,365	19,229
Deposits
Demand deposits	53,547,761	54,445,825
Time deposits	7,019,993	6,464,943
Deposits	60,567,754	60,910,768
Assets sold under agreements to repurchase	123,487	148,566
Other short-term borrowings	0	365,000
Notes payable:
FHLB advances	365,862	361,951
Unsecured senior debt securities	693,253	300,027
Junior subordinated deferrable interest debentures (related to trust preferred securities)	177,823	173,938
Notes payable	1,236,938	835,916
Derivatives	17,115	17,000
Fair Value | US Treasury Securities
Financial Assets:
Debt securities held-to-maturity	8,534,105	8,372,601
Fair Value | Obligations of Puerto Rico, States and political subdivisions
Financial Assets:
Debt securities held-to-maturity	57,839	61,617
Fair Value | Collateralized Mortgage Obligations - Federal agencies
Financial Assets:
Debt securities held-to-maturity	16	19
Fair Value | Securities in wholly owned statutory business trusts
Financial Assets:
Debt securities held-to-maturity	5,959	5,959
Fair Value | Level 1
Financial Assets:
Cash and due from banks	462,013	469,501
Money market investments	6,091,115	5,607,937
Trading account debt securities, excluding derivatives	15,462	13,069
Debt securities available-for-sale	1,865,470	1,908,589
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	7,173	6,658
Trading account debt securities, excluding derivatives	13,886	14,119
Debt securities available-for-sale	15,306,003	15,894,074
Debt securities held-to-maturity	8,540,064	8,378,560
Equity securities:
FHLB stock	49,265	65,861
FRB stock	99,134	96,206
Other investments	32,545	29,302
Equity securities, at lower of cost or realizable value	180,944	191,369
Loans held-for-sale	11,181	0
Loans held in portfolio	0	0
Mortgage servicing rights	0	0
Derivatives	19,365	19,229
Deposits
Demand deposits	53,547,761	54,445,825
Time deposits	7,019,993	6,464,943
Deposits	60,567,754	60,910,768
Assets sold under agreements to repurchase	123,487	148,566
Other short-term borrowings	0	365,000
Notes payable:
FHLB advances	365,862	361,951
Unsecured senior debt securities	693,253	300,027
Junior subordinated deferrable interest debentures (related to trust preferred securities)	177,823	173,938
Notes payable	1,236,938	835,916
Derivatives	17,115	17,000
Fair Value | Level 2 | US Treasury Securities
Financial Assets:
Debt securities held-to-maturity	8,534,105	8,372,601
Fair Value | Level 2 | Obligations of Puerto Rico, States and political subdivisions
Financial Assets:
Debt securities held-to-maturity	0	0
Fair Value | Level 2 | Collateralized Mortgage Obligations - Federal agencies
Financial Assets:
Debt securities held-to-maturity	0	0
Fair Value | Level 2 | Securities in wholly owned statutory business trusts
Financial Assets:
Debt securities held-to-maturity	5,959	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	475	535
Debt securities available-for-sale	1,655	1,711
Debt securities held-to-maturity	57,855	61,636
Equity securities:
FHLB stock	0	0
FRB stock	0	0
Other investments	5,482	4,966
Equity securities, at lower of cost or realizable value	5,482	4,966
Loans held-for-sale	0	5,404
Loans held in portfolio	30,066,069	29,366,365
Mortgage servicing rights	127,475	128,350
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	57,839	61,617
Fair Value | Level 3 | Collateralized Mortgage Obligations - Federal agencies
Financial Assets:
Debt securities held-to-maturity	16	19
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	318	330
Equity securities, at lower of cost or realizable value	318	330
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