Income taxes - Components of deferred tax assets and liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Deferred tax assets:
Tax credits available for carryforward	$ 20,455	$ 10,544
Net operating loss and other carryforward available	664,108	743,616
Postretirement and pension benefits	36,895	38,121
Allowance for credit losses	273,354	273,178
Depreciation	13,638	13,352
Deferred loan origination fees/cost	147
FDIC-assisted transaction	152,665	152,665
Lease liability	43,051	49,562
Unrealized net loss on investment securities	251,348	331,620
Difference in outside basis from pass-through entities	47,413	46,056
Mortgage servicing rights	14,854	14,085
Other temporary differences	53,787	57,304
Total gross deferred tax assets	1,571,715	1,730,103
Deferred tax liabilities:
Intangibles	141,678	136,579
Right of use assets	38,531	44,678
Deferred loan origination fees/cost		430
Loans acquired	17,123	20,430
Other temporary differences	7,561	6,824
Total gross deferred tax liabilities	204,893	208,941
Valuation allowance	450,507	513,382
Net deferred tax asset	916,315	1,007,780
PR
Deferred tax assets:
Tax credits available for carryforward	263	263
Net operating loss and other carryforward available	54,294	122,634
Postretirement and pension benefits	36,895	38,121
Allowance for credit losses	248,766	244,956
Depreciation	6,774	6,774
Deferred loan origination fees/cost	2,470
FDIC-assisted transaction	152,665	152,665
Lease liability	26,138	29,070
Unrealized net loss on investment securities	237,859	312,583
Difference in outside basis from pass-through entities	47,413	46,056
Mortgage servicing rights	14,854	14,085
Other temporary differences	44,651	47,679
Total gross deferred tax assets	873,042	1,014,886
Deferred tax liabilities:
Intangibles	87,422	84,635
Right of use assets	23,725	26,648
Deferred loan origination fees/cost		(1,056)
Loans acquired	17,123	20,430
Other temporary differences	7,139	6,402
Total gross deferred tax liabilities	135,409	137,059
Valuation allowance	71,596	139,347
Net deferred tax asset	666,037	738,480
US
Deferred tax assets:
Tax credits available for carryforward	20,192	10,281
Net operating loss and other carryforward available	609,814	620,982
Postretirement and pension benefits	0	0
Allowance for credit losses	24,588	28,222
Depreciation	6,864	6,578
Deferred loan origination fees/cost	(2,323)
FDIC-assisted transaction	0	0
Lease liability	16,913	20,492
Unrealized net loss on investment securities	13,489	19,037
Difference in outside basis from pass-through entities	0	0
Mortgage servicing rights	0	0
Other temporary differences	9,136	9,625
Total gross deferred tax assets	698,673	715,217
Deferred tax liabilities:
Intangibles	54,256	51,944
Right of use assets	14,806	18,030
Deferred loan origination fees/cost		1,486
Loans acquired	0	0
Other temporary differences	422	422
Total gross deferred tax liabilities	69,484	71,882
Valuation allowance	378,911	374,035
Net deferred tax asset	$ 250,278	$ 269,300