Income taxes - Components of deferred tax assets and liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Deferred tax assets:
Tax credits available for carryforward	$ 3,042	$ 3,042
Net operating loss and other carryforward available	782,886	777,495
Postretirement and pension benefits	47,122	57,002
Deferred loan origination fees/cost		2,788
Allowance for credit losses	283,303	265,372
Deferred gains		1,642
Accelerated depreciation	12,281	12,668
FDIC-assisted transaction	152,665	152,665
Intercompany deferred gains	1,548
Lease liability	51,811	55,105
Unrealized net loss on investment securities	289,868
Difference in outside basis from pass-through entities	40,602	54,781
Other temporary differences	37,100	46,930
Total gross deferred tax assets	1,702,228	1,429,490
Deferred tax liabilities:
Intangibles	135,797	127,785
Unrealized net gain on investment securities		7,146
Right of use assets	46,277	49,307
Deferred loan origination fees/cost	4,037	3,567
Other temporary differences	24,884	45,386
Total gross deferred tax liabilities	210,995	233,191
Valuation allowance	540,196	539,527
Net deferred tax asset	951,037	656,772
PR
Deferred tax assets:
Tax credits available for carryforward	261	261
Net operating loss and other carryforward available	121,742	112,331
Postretirement and pension benefits	47,122	57,002
Deferred loan origination fees/cost		2,788
Allowance for credit losses	250,615	233,500
Deferred gains		1,642
Accelerated depreciation	5,972	5,246
FDIC-assisted transaction	152,665	152,665
Intercompany deferred gains	1,548
Lease liability	28,290	31,211
Unrealized net loss on investment securities	265,955
Difference in outside basis from pass-through entities	40,602	54,781
Other temporary differences	29,285	38,512
Total gross deferred tax assets	944,057	689,939
Deferred tax liabilities:
Intangibles	81,174	76,635
Unrealized net gain on investment securities		4,329
Right of use assets	26,015	29,025
Deferred loan origination fees/cost	1,076	0
Other temporary differences	24,884	43,856
Total gross deferred tax liabilities	133,149	153,845
Valuation allowance	137,863	128,557
Net deferred tax asset	673,045	407,537
US
Deferred tax assets:
Tax credits available for carryforward	2,781	2,781
Net operating loss and other carryforward available	661,144	665,164
Postretirement and pension benefits	0	0
Deferred loan origination fees/cost		0
Allowance for credit losses	32,688	31,872
Deferred gains		0
Accelerated depreciation	6,309	7,422
FDIC-assisted transaction	0	0
Intercompany deferred gains	0
Lease liability	23,521	23,894
Unrealized net loss on investment securities	23,913
Difference in outside basis from pass-through entities	0	0
Other temporary differences	7,815	8,418
Total gross deferred tax assets	758,171	739,551
Deferred tax liabilities:
Intangibles	54,623	51,150
Unrealized net gain on investment securities		2,817
Right of use assets	20,262	20,282
Deferred loan origination fees/cost	2,961	3,567
Other temporary differences	0	1,530
Total gross deferred tax liabilities	77,846	79,346
Valuation allowance	402,333	410,970
Net deferred tax asset	$ 277,992	$ 249,235