Income taxes - Components of deferred tax assets and liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Deferred tax assets:
Tax credits available for carryforward	$ 14,467	$ 10,544
Net operating loss and other carryforward available	670,022	743,616
Postretirement and pension benefits	37,219	38,121
Allowance for credit losses	270,313	273,178
Depreciation	13,520	13,352
FDIC-assisted transaction	152,665	152,665
Lease liability	45,295	49,562
Unrealized net loss on investment securities	315,246	331,620
Difference in outside basis from pass-through entities	45,207	46,056
Mortgage servicing rights	14,063	14,085
Other temporary differences	57,497	57,304
Total gross deferred tax assets	1,635,514	1,730,103
Deferred tax liabilities:
Intangibles	139,978	136,579
Right of use assets	40,675	44,678
Deferred loan origination fees/cost	1,320	430
Loans acquired	18,229	20,430
Other temporary differences	7,353	6,824
Total gross deferred tax liabilities	207,555	208,941
Valuation allowance	450,057	513,382
Net deferred tax asset	977,902	1,007,780
PR
Deferred tax assets:
Tax credits available for carryforward	263	263
Net operating loss and other carryforward available	53,942	122,634
Postretirement and pension benefits	37,219	38,121
Allowance for credit losses	242,722	244,956
Depreciation	6,774	6,774
FDIC-assisted transaction	152,665	152,665
Lease liability	27,196	29,070
Unrealized net loss on investment securities	294,942	312,583
Difference in outside basis from pass-through entities	45,207	46,056
Mortgage servicing rights	14,063	14,085
Other temporary differences	47,615	47,679
Total gross deferred tax assets	922,608	1,014,886
Deferred tax liabilities:
Intangibles	86,493	84,635
Right of use assets	24,764	26,648
Deferred loan origination fees/cost	(749)	(1,056)
Loans acquired	18,229	20,430
Other temporary differences	6,931	6,402
Total gross deferred tax liabilities	135,668	137,059
Valuation allowance	71,145	139,347
Net deferred tax asset	715,795	738,480
US
Deferred tax assets:
Tax credits available for carryforward	14,204	10,281
Net operating loss and other carryforward available	616,080	620,982
Postretirement and pension benefits	0	0
Allowance for credit losses	27,591	28,222
Depreciation	6,746	6,578
FDIC-assisted transaction	0	0
Lease liability	18,099	20,492
Unrealized net loss on investment securities	20,304	19,037
Difference in outside basis from pass-through entities	0	0
Mortgage servicing rights	0	0
Other temporary differences	9,882	9,625
Total gross deferred tax assets	712,906	715,217
Deferred tax liabilities:
Intangibles	53,485	51,944
Right of use assets	15,911	18,030
Deferred loan origination fees/cost	2,069	1,486
Loans acquired	0	0
Other temporary differences	422	422
Total gross deferred tax liabilities	71,887	71,882
Valuation allowance	378,912	374,035
Net deferred tax asset	$ 262,107	$ 269,300