Income taxes - Components of deferred tax assets and liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Deferred tax assets:
Tax credits available for carryforward	$ 7,195	$ 3,042
Net operating loss and other carryforward available	772,266	782,886
Postretirement and pension benefits	46,920	47,122
Allowance for credit losses	268,972	283,303
Depreciation	12,378	12,281
FDIC-assisted transaction	152,665	152,665
Lease liability	50,299	51,811
Unrealized net loss on investment securities	258,059	289,868
Difference in outside basis from pass-through entities	32,234	40,602
Mortgage servicing rights	14,700	13,711
Other temporary differences	39,292	24,937
Total gross deferred tax assets	1,654,980	1,702,228
Deferred tax liabilities:
Intangibles	139,241	135,797
Right of use assets	45,139	46,277
Deferred loan origination fees/cost	4,574	4,037
Loans acquired	20,914	23,353
Other temporary differences	6,944	1,531
Total gross deferred tax liabilities	216,812	210,995
Valuation allowance	537,185	540,196
Net deferred tax asset	900,983	951,037
PR
Deferred tax assets:
Tax credits available for carryforward	261	261
Net operating loss and other carryforward available	122,293	121,742
Postretirement and pension benefits	46,920	47,122
Allowance for credit losses	238,377	250,615
Depreciation	6,033	5,972
FDIC-assisted transaction	152,665	152,665
Lease liability	29,241	28,290
Unrealized net loss on investment securities	235,339	265,955
Difference in outside basis from pass-through entities	32,234	40,602
Mortgage servicing rights	14,700	13,711
Other temporary differences	30,222	17,122
Total gross deferred tax assets	908,285	944,057
Deferred tax liabilities:
Intangibles	83,032	81,174
Right of use assets	26,856	26,015
Deferred loan origination fees/cost	2,096	1,076
Loans acquired	20,914	23,353
Other temporary differences	6,522	1,531
Total gross deferred tax liabilities	139,420	133,149
Valuation allowance	138,825	137,863
Net deferred tax asset	630,040	673,045
US
Deferred tax assets:
Tax credits available for carryforward	6,934	2,781
Net operating loss and other carryforward available	649,973	661,144
Postretirement and pension benefits	0	0
Allowance for credit losses	30,595	32,688
Depreciation	6,345	6,309
FDIC-assisted transaction	0	0
Lease liability	21,058	23,521
Unrealized net loss on investment securities	22,720	23,913
Difference in outside basis from pass-through entities	0	0
Mortgage servicing rights	0	0
Other temporary differences	9,070	7,815
Total gross deferred tax assets	746,695	758,171
Deferred tax liabilities:
Intangibles	56,209	54,623
Right of use assets	18,283	20,262
Deferred loan origination fees/cost	2,478	2,961
Loans acquired	0	0
Other temporary differences	422	0
Total gross deferred tax liabilities	77,392	77,846
Valuation allowance	398,360	402,333
Net deferred tax asset	$ 270,943	$ 277,992