Income taxes - Components of deferred tax assets and liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Deferred tax assets:
Tax credits available for carryforward	$ 29,589	$ 10,544
Net operating loss and other carryforward available	662,490	743,616
Postretirement and pension benefits	27,786	38,121
Allowance for credit losses	271,568	273,178
Depreciation	14,929	13,352
FDIC-assisted transaction	152,665	152,665
Lease liability	41,618	49,562
Unrealized net loss on investment securities	273,407	331,620
Difference in outside basis from pass-through entities	50,144	46,056
Mortgage servicing rights	14,475	14,085
Other temporary differences	50,199	57,304
Total gross deferred tax assets	1,588,870	1,730,103
Deferred tax liabilities:
Intangibles	144,277	136,579
Right of use assets	37,238	44,678
Deferred loan origination fees/cost	205	430
Loans acquired	18,415	20,430
Other temporary differences	7,228	6,824
Total gross deferred tax liabilities	207,363	208,941
Valuation allowance	456,751	513,382
Net deferred tax asset	924,756	1,007,780
PR
Deferred tax assets:
Tax credits available for carryforward	4,861	263
Net operating loss and other carryforward available	52,211	122,634
Postretirement and pension benefits	27,786	38,121
Allowance for credit losses	247,153	244,956
Depreciation	7,700	6,774
FDIC-assisted transaction	152,665	152,665
Lease liability	25,167	29,070
Unrealized net loss on investment securities	252,411	312,583
Difference in outside basis from pass-through entities	50,144	46,056
Mortgage servicing rights	14,475	14,085
Other temporary differences	41,127	47,679
Total gross deferred tax assets	875,700	1,014,886
Deferred tax liabilities:
Intangibles	88,351	84,635
Right of use assets	22,784	26,648
Deferred loan origination fees/cost	(1,880)	(1,056)
Loans acquired	18,415	20,430
Other temporary differences	6,799	6,402
Total gross deferred tax liabilities	134,469	137,059
Valuation allowance	69,837	139,347
Net deferred tax asset	671,394	738,480
US
Deferred tax assets:
Tax credits available for carryforward	24,728	10,281
Net operating loss and other carryforward available	610,279	620,982
Postretirement and pension benefits	0	0
Allowance for credit losses	24,415	28,222
Depreciation	7,229	6,578
FDIC-assisted transaction	0	0
Lease liability	16,451	20,492
Unrealized net loss on investment securities	20,996	19,037
Difference in outside basis from pass-through entities	0	0
Mortgage servicing rights	0	0
Other temporary differences	9,072	9,625
Total gross deferred tax assets	713,170	715,217
Deferred tax liabilities:
Intangibles	55,926	51,944
Right of use assets	14,454	18,030
Deferred loan origination fees/cost	2,085	1,486
Loans acquired	0	0
Other temporary differences	429	422
Total gross deferred tax liabilities	72,894	71,882
Valuation allowance	386,914	374,035
Net deferred tax asset	$ 253,362	$ 269,300