Allowance for loan losses - Average recorded investment and interest income recognized on impaired loans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Financing Receivable, Impaired
Average Recorded Investment	$ 1,039,266	$ 996,030	$ 1,041,205	$ 979,826
Interest Income Recognized	9,049	7,926	17,312	18,291
Commercial multi-family | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	2,239	414	1,803	344
Interest Income Recognized	12	0	24	0
CRE non-owner occupied | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	176,552	132,842	178,230	126,208
Interest Income Recognized	2,512	1,681	4,361	3,104
CRE owner occupied | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	140,118	153,007	140,100	152,761
Interest Income Recognized	1,671	1,596	3,173	3,195
Commercial and industrial | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	67,976	69,493	70,628	65,676
Interest Income Recognized	725	702	1,512	1,397
Construction | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	13,848	12,377	13,848	8,251
Interest Income Recognized	0	0	0	25
Mortgages | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	527,727	518,616	524,780	518,502
Interest Income Recognized	4,060	3,832	8,098	10,316
Leasing | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	942	1,246	994	1,316
Interest Income Recognized	0	0	0	0
Consumer | Credit cards | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	27,261	33,293	27,784	33,421
Interest Income Recognized	0	0	0	0
Consumer | Home equity lines of credit | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	9,013	5,436	8,586	5,054
Interest Income Recognized	0	0	0	0
Consumer | Personal Loan | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	71,289	66,569	72,113	65,463
Interest Income Recognized	69	115	144	254
Consumer | Auto Loan | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	1,157	1,399	1,158	1,602
Interest Income Recognized	0	0	0	0
Consumer | Other | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	1,144	1,338	1,181	1,228
Interest Income Recognized	0	0	0	0
PUERTO RICO
Financing Receivable, Impaired
Average Recorded Investment	1,005,494	971,469	1,008,696	958,687
Interest Income Recognized	9,015	7,883	17,239	18,204
PUERTO RICO | Commercial multi-family | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	978	414	963	344
Interest Income Recognized	12	0	24	0
PUERTO RICO | CRE non-owner occupied | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	176,552	132,842	178,230	126,208
Interest Income Recognized	2,512	1,681	4,361	3,104
PUERTO RICO | CRE owner occupied | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	138,552	153,007	139,056	152,761
Interest Income Recognized	1,671	1,596	3,173	3,195
PUERTO RICO | Commercial and industrial | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	67,976	69,493	70,628	65,676
Interest Income Recognized	725	702	1,512	1,397
PUERTO RICO | Construction | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	1,788	3,426	1,788	2,284
Interest Income Recognized	0	0	0	25
PUERTO RICO | Mortgages | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	518,311	509,215	515,363	509,154
Interest Income Recognized	4,026	3,789	8,025	10,229
PUERTO RICO | Leasing | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	942	1,246	994	1,316
Interest Income Recognized	0	0	0	0
PUERTO RICO | Consumer | Credit cards | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	27,261	33,293	27,784	33,421
Interest Income Recognized	0	0	0	0
PUERTO RICO | Consumer | Home equity lines of credit | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	0	0	0	0
Interest Income Recognized	0	0	0	0
PUERTO RICO | Consumer | Personal Loan | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	70,833	65,796	71,551	64,693
Interest Income Recognized	69	115	144	254
PUERTO RICO | Consumer | Auto Loan | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	1,157	1,399	1,158	1,602
Interest Income Recognized	0	0	0	0
PUERTO RICO | Consumer | Other | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	1,144	1,338	1,181	1,228
Interest Income Recognized	0	0	0	0
UNITED STATES
Financing Receivable, Impaired
Average Recorded Investment	33,772	24,561	32,509	21,139
Interest Income Recognized	34	43	73	87
UNITED STATES | Commercial multi-family | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	1,261	0	840	0
Interest Income Recognized	0	0	0	0
UNITED STATES | CRE non-owner occupied | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	0	0	0	0
Interest Income Recognized	0	0	0	0
UNITED STATES | CRE owner occupied | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	1,566	0	1,044	0
Interest Income Recognized	0	0	0	0
UNITED STATES | Commercial and industrial | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	0	0	0	0
Interest Income Recognized	0	0	0	0
UNITED STATES | Construction | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	12,060	8,951	12,060	5,967
Interest Income Recognized	0	0	0	0
UNITED STATES | Mortgages | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	9,416	9,401	9,417	9,348
Interest Income Recognized	34	43	73	87
UNITED STATES | Leasing | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	0	0	0	0
Interest Income Recognized	0	0	0	0
UNITED STATES | Consumer | Credit cards | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	0	0	0	0
Interest Income Recognized	0	0	0	0
UNITED STATES | Consumer | Home equity lines of credit | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	9,013	5,436	8,586	5,054
Interest Income Recognized	0	0	0	0
UNITED STATES | Consumer | Personal Loan | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	456	773	562	770
Interest Income Recognized	0	0	0	0
UNITED STATES | Consumer | Auto Loan | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	0	0	0	0
Interest Income Recognized	0	0	0	0
UNITED STATES | Consumer | Other | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	0	0	0	0
Interest Income Recognized	$ 0	$ 0	$ 0	$ 0