Allowance for loan losses - Average recorded investment and interest income recognized on impaired loans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Financing Receivable, Impaired
Average Recorded Investment	$ 1,051,553	$ 1,009,563	$ 1,045,561	$ 986,943
Interest Income Recognized	9,777	7,738	27,525	26,150
Commercial multi-family | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	3,950	1,100	2,439	634
Interest Income Recognized	12	9	36	28
CRE non-owner occupied | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	182,078	132,927	180,401	128,143
Interest Income Recognized	2,561	1,371	6,987	4,278
CRE owner occupied | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	139,045	148,931	139,869	151,192
Interest Income Recognized	1,698	1,636	4,831	4,786
Commercial and industrial | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	74,674	74,770	72,668	67,775
Interest Income Recognized	888	1,053	2,744	2,793
Construction | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	12,091	20,078	12,970	11,112
Interest Income Recognized	0	0	0	25
Mortgages | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	531,984	517,196	526,915	518,147
Interest Income Recognized	4,554	3,604	12,719	13,920
Leasing | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	745	1,031	902	1,220
Interest Income Recognized	0	0	0	0
Consumer | Credit cards | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	26,346	31,998	27,350	32,734
Interest Income Recognized	0	0	0	0
Consumer | Home equity lines of credit | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	9,749	6,208	8,855	5,446
Interest Income Recognized	0	0	0	0
Consumer | Personal Loan | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	69,210	73,121	71,147	67,818
Interest Income Recognized	64	65	208	320
Consumer | Auto Loan | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	742	1,067	952	1,476
Interest Income Recognized	0	0	0	0
Consumer | Other | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	939	1,136	1,093	1,246
Interest Income Recognized	0	0	0	0
PUERTO RICO
Financing Receivable, Impaired
Average Recorded Investment	1,018,191	975,426	1,013,338	962,569
Interest Income Recognized	9,622	7,695	27,229	26,020
PUERTO RICO | Commercial multi-family | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	1,641	1,100	1,284	634
Interest Income Recognized	12	9	36	28
PUERTO RICO | CRE non-owner occupied | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	182,078	132,927	180,401	128,143
Interest Income Recognized	2,561	1,371	6,987	4,278
PUERTO RICO | CRE owner occupied | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	138,325	148,931	139,086	151,192
Interest Income Recognized	1,698	1,636	4,831	4,786
PUERTO RICO | Commercial and industrial | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	74,674	74,770	72,668	67,775
Interest Income Recognized	888	1,053	2,744	2,793
PUERTO RICO | Construction | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	1,031	2,194	1,410	2,170
Interest Income Recognized	0	0	0	25
PUERTO RICO | Mortgages | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	522,567	507,919	517,492	508,930
Interest Income Recognized	4,399	3,561	12,423	13,790
PUERTO RICO | Leasing | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	745	1,031	902	1,220
Interest Income Recognized	0	0	0	0
PUERTO RICO | Consumer | Credit cards | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	26,346	31,998	27,350	32,734
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	69,103	72,353	70,700	67,049
Interest Income Recognized	64	65	208	320
PUERTO RICO | Consumer | Auto Loan | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	742	1,067	952	1,476
Interest Income Recognized	0	0	0	0
PUERTO RICO | Consumer | Other | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	939	1,136	1,093	1,246
Interest Income Recognized	0	0	0	0
UNITED STATES
Financing Receivable, Impaired
Average Recorded Investment	33,362	34,137	32,223	24,374
Interest Income Recognized	155	43	296	130
UNITED STATES | Commercial multi-family | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	2,309	0	1,155	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	720	0	783	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	11,060	17,884	11,560	8,942
Interest Income Recognized	0	0	0	0
UNITED STATES | Mortgages | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	9,417	9,277	9,423	9,217
Interest Income Recognized	155	43	296	130
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	9,749	6,208	8,855	5,446
Interest Income Recognized	0	0	0	0
UNITED STATES | Consumer | Personal Loan | Non Covered Loans
Financing Receivable, Impaired
Average Recorded Investment	107	768	447	769
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