Income taxes - Components of deferred tax assets and liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Deferred tax assets:
Tax credits available for carryforward	$ 11,015	$ 3,042
Net operating loss and other carryforward available	767,203	782,886
Postretirement and pension benefits	46,823	47,122
Allowance for credit losses	268,461	283,303
Depreciation	12,417	12,281
FDIC-assisted transaction	152,665	152,665
Lease liability	49,293	51,811
Unrealized net loss on investment securities	245,985	289,868
Difference in outside basis from pass-through entities	38,439	40,602
Mortgage servicing rights	14,685	13,711
Other temporary differences	38,199	24,937
Total gross deferred tax assets	1,645,185	1,702,228
Deferred tax liabilities:
Intangibles	134,353	135,797
Right of use assets	44,161	46,277
Deferred loan origination fees/cost	3,934	4,037
Loans acquired	19,698	23,353
Other temporary differences	6,475	1,531
Total gross deferred tax liabilities	208,621	210,995
Valuation allowance	541,351	540,196
Net deferred tax asset	895,213	951,037
PR
Deferred tax assets:
Tax credits available for carryforward	261	261
Net operating loss and other carryforward available	123,196	121,742
Postretirement and pension benefits	46,823	47,122
Allowance for credit losses	242,095	250,615
Depreciation	5,972	5,972
FDIC-assisted transaction	152,665	152,665
Lease liability	29,056	28,290
Unrealized net loss on investment securities	218,866	265,955
Difference in outside basis from pass-through entities	38,439	40,602
Mortgage servicing rights	14,685	13,711
Other temporary differences	30,804	17,122
Total gross deferred tax assets	902,862	944,057
Deferred tax liabilities:
Intangibles	83,961	81,174
Right of use assets	26,655	26,015
Deferred loan origination fees/cost	1,990	1,076
Loans acquired	19,698	23,353
Other temporary differences	6,053	1,531
Total gross deferred tax liabilities	138,357	133,149
Valuation allowance	140,033	137,863
Net deferred tax asset	624,472	673,045
US
Deferred tax assets:
Tax credits available for carryforward	10,754	2,781
Net operating loss and other carryforward available	644,007	661,144
Postretirement and pension benefits	0	0
Allowance for credit losses	26,366	32,688
Depreciation	6,445	6,309
FDIC-assisted transaction	0	0
Lease liability	20,237	23,521
Unrealized net loss on investment securities	27,119	23,913
Difference in outside basis from pass-through entities	0	0
Mortgage servicing rights	0	0
Other temporary differences	7,395	7,815
Total gross deferred tax assets	742,323	758,171
Deferred tax liabilities:
Intangibles	50,392	54,623
Right of use assets	17,506	20,262
Deferred loan origination fees/cost	1,944	2,961
Loans acquired	0	0
Other temporary differences	422	0
Total gross deferred tax liabilities	70,264	77,846
Valuation allowance	401,318	402,333
Net deferred tax asset	$ 270,741	$ 277,992