Income taxes - Components of deferred tax assets and liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Deferred tax assets:
Tax credits available for carryforward	$ 8,272	$ 7,637
Net operating loss and other carryforward available	823,575	829,599
Postretirement and pension benefits	78,175	82,623
Allowance for credit losses	448,133	416,456
Accelerated depreciation	8,428	8,353
FDIC-assisted transaction	82,994	82,684
Lease liability	44,637	46,081
Difference in outside basis from pass-through entities	59,348	21,670
Other temporary differences	45,784	34,014
Total gross deferred tax assets	1,613,756	1,530,481
Deferred tax liabilities:
Indefinite-lived intangibles	77,570	73,469
Unrealized net gain (loss) on trading and available-for-sale securities	82,894	16,067
Right of use assets	40,678	42,028
Other temporary differences	14,655	13,957
Total gross deferred tax liabilities	215,797	145,521
Valuation allowance	517,025	499,975
Net deferred tax asset	880,934	884,985
PUERTO RICO
Deferred tax assets:
Tax credits available for carryforward	3,003	2,368
Net operating loss and other carryforward available	121,842	112,803
Postretirement and pension benefits	78,175	82,623
Allowance for credit losses	405,681	405,475
Accelerated depreciation	3,439	3,439
FDIC-assisted transaction	82,994	82,684
Lease liability	23,350	22,694
Difference in outside basis from pass-through entities	59,348	21,670
Other temporary differences	37,883	26,554
Total gross deferred tax assets	832,578	764,433
Deferred tax liabilities:
Indefinite-lived intangibles	39,908	37,411
Unrealized net gain (loss) on trading and available-for-sale securities	74,101	15,635
Right of use assets	21,266	20,598
Other temporary differences	13,473	12,778
Total gross deferred tax liabilities	148,748	86,422
Valuation allowance	110,435	100,175
Net deferred tax asset	573,395	577,836
UNITED STATES
Deferred tax assets:
Tax credits available for carryforward	5,269	5,269
Net operating loss and other carryforward available	701,733	716,796
Postretirement and pension benefits	0	0
Allowance for credit losses	42,452	10,981
Accelerated depreciation	4,989	4,914
FDIC-assisted transaction	0	0
Lease liability	21,287	23,387
Difference in outside basis from pass-through entities	0	0
Other temporary differences	7,901	7,460
Total gross deferred tax assets	781,178	766,048
Deferred tax liabilities:
Indefinite-lived intangibles	37,662	36,058
Unrealized net gain (loss) on trading and available-for-sale securities	8,793	432
Right of use assets	19,412	21,430
Other temporary differences	1,182	1,179
Total gross deferred tax liabilities	67,049	59,099
Valuation allowance	406,590	399,800
Net deferred tax asset	307,539	307,149
Deferred loans origination fees
Deferred tax assets:
Deferred income	12,957	(240)
Deferred loans origination fees | PUERTO RICO
Deferred tax assets:
Deferred income	15,410	2,519
Deferred loans origination fees | UNITED STATES
Deferred tax assets:
Deferred income	(2,453)	(2,759)
Intercompany deferred gains
Deferred tax assets:
Deferred income	1,453	1,604
Intercompany deferred gains | PUERTO RICO
Deferred tax assets:
Deferred income	1,453	1,604
Intercompany deferred gains | UNITED STATES
Deferred tax assets:
Deferred income	$ 0	$ 0