Commitments and contingencies - Commitments - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		12 Months Ended
	Jul. 31, 2024	Mar. 31, 2024	Dec. 31, 2023	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Commitments and Contingencies Disclosure [Line Items]
Loans And Leases Receivable Gross Carrying Amount			$ 35,420,879	$ 37,522,995	$ 35,420,879
FDIC deposit insurance expense				54,626	105,985	$ 26,787
FDIC Special Assessment
Commitments and Contingencies Disclosure [Line Items]
FDIC Indemnification Asset		$ 20,400,000	16,300,000		16,300,000
FDIC deposit insurance expense		14,300	71,400
FDIC deposit insurance expense net of tax		$ 9,100	45,300
Commitments to extend credit
Commitments and Contingencies Disclosure [Line Items]
Reserve of potential losses associated with unfunded loan commitments			17,000	15,000	17,000
Noncredit commitment
Commitments and Contingencies Disclosure [Line Items]
Investments			3,300	2,000	3,300
Residential mortgage loans
Commitments and Contingencies Disclosure [Line Items]
Loans And Leases Receivable Gross Carrying Amount			1,900,000	2,100,000	1,900,000
BVI | Retail and commerical loans
Commitments and Contingencies Disclosure [Line Items]
Loans And Leases Receivable Gross Carrying Amount			205,000	196,000	205,000
Insured or guaranteed by the U.S. Government or its agencies | Commercial Loans
Commitments and Contingencies Disclosure [Line Items]
Loans And Leases Receivable Gross Carrying Amount			89,200	87,400	89,200
PR Government direct exposure
Commitments and Contingencies Disclosure [Line Items]
Total concentration of risk				336,113	362,000
Outstanding concentration of risk			333,000	$ 336,113	333,000
Exposure Municipal Loans And Securities				80.00%
Principal payment from various obligations	$ 40,000
PR Government direct exposure | Loans
Commitments and Contingencies Disclosure [Line Items]
Outstanding concentration of risk			314,000	$ 323,452	314,000
PR Government direct exposure | Securities Investment
Commitments and Contingencies Disclosure [Line Items]
Outstanding concentration of risk			19,000	12,661	19,000
PR Government Indirect Exposure
Commitments and Contingencies Disclosure [Line Items]
Outstanding concentration of risk			238,000	220,000	238,000
Loans and Leases Receivable, Consumer, Mortgage with PRHA			191,000	176,000	191,000
PR Government Indirect Exposure | PR Housing Bonds backed by second mortgage loans
Commitments and Contingencies Disclosure [Line Items]
Outstanding concentration of risk			$ 40,000	38,000	40,000
USVI Government Direct Exposure | From USVI Government And Public Corporations
Commitments and Contingencies Disclosure [Line Items]
Total concentration of risk				$ 28,000	$ 28,000