Note Allowance for loan losses (Average recorded investment and interest income recognized on impaired loans) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	$ 1,009,563	$ 955,782	$ 986,943	$ 959,458
Interest Income Recognized	7,738	6,488	26,150	21,873
Commercial multi-family | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	1,100	141	634	111
Interest Income Recognized	9	1	28	4
CRE non-owner occupied | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	132,927	117,650	128,143	118,243
Interest Income Recognized	1,371	1,272	4,278	3,997
CRE owner occupied | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	148,931	151,580	151,192	158,046
Interest Income Recognized	1,636	1,413	4,786	4,640
Commercial and industrial | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	74,770	61,950	67,775	61,072
Interest Income Recognized	1,053	531	2,793	1,682
Construction | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	20,078		11,112
Interest Income Recognized	0		25
Mortgages | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	517,196	516,684	518,147	512,575
Interest Income Recognized	3,604	3,271	13,920	11,550
Leasing | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	1,031	1,568	1,220	1,689
Interest Income Recognized	0	0	0	0
Consumer | Credit cards | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	31,998	35,727	32,734	36,718
Interest Income Recognized	0	0	0	0
Consumer | Home equity lines of credit | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	6,208	2,572	5,446	2,632
Interest Income Recognized	0	0	0	0
Consumer | Personal | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	73,121	64,854	67,818	65,402
Interest Income Recognized	65	0	320	0
Consumer | Auto Loan | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	1,067	2,065	1,476	2,079
Interest Income Recognized	0	0	0	0
Consumer | Other | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	1,136	991	1,246	891
Interest Income Recognized	0	0	0	0
PUERTO RICO
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	975,426	943,452	962,569	947,439
Interest Income Recognized	7,695	6,428	26,020	21,717
PUERTO RICO | Commercial multi-family | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	1,100	141	634	111
Interest Income Recognized	9	1	28	4
PUERTO RICO | CRE non-owner occupied | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	132,927	117,650	128,143	118,243
Interest Income Recognized	1,371	1,272	4,278	3,997
PUERTO RICO | CRE owner occupied | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	148,931	151,580	151,192	158,046
Interest Income Recognized	1,636	1,413	4,786	4,640
PUERTO RICO | Commercial and industrial | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	74,770	61,950	67,775	61,072
Interest Income Recognized	1,053	531	2,793	1,682
PUERTO RICO | Construction | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	2,194		2,170
Interest Income Recognized	0		25
PUERTO RICO | Mortgages | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	507,919	507,689	508,930	503,628
Interest Income Recognized	3,561	3,211	13,790	11,394
PUERTO RICO | Leasing | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	1,031	1,568	1,220	1,689
Interest Income Recognized	0	0	0	0
PUERTO RICO | Consumer | Credit cards | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	31,998	35,727	32,734	36,718
Interest Income Recognized	0	0	0	0
PUERTO RICO | Consumer | Home equity lines of credit | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	0	0	0	0
Interest Income Recognized	0	0	0	0
PUERTO RICO | Consumer | Personal | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	72,353	64,091	67,049	64,962
Interest Income Recognized	65	0	320	0
PUERTO RICO | Consumer | Auto Loan | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	1,067	2,065	1,476	2,079
Interest Income Recognized	0	0	0	0
PUERTO RICO | Consumer | Other | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	1,136	991	1,246	891
Interest Income Recognized	0	0	0	0
UNITED STATES
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	34,137	12,330	24,374	12,019
Interest Income Recognized	43	60	130	156
UNITED STATES | Commercial multi-family | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	0	0	0	0
Interest Income Recognized	0	0	0	0
UNITED STATES | CRE non-owner occupied | Non Covered Loans
Financing Receivable, Impaired [Line Items]
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 [Line Items]
Average Recorded Investment	0	0	0	0
Interest Income Recognized	0	0	0	0
UNITED STATES | Commercial and industrial | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	0	0	0	0
Interest Income Recognized	0	0	0	0
UNITED STATES | Construction | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	17,884		8,942
Interest Income Recognized	0		0
UNITED STATES | Mortgages | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	9,277	8,995	9,217	8,947
Interest Income Recognized	43	60	130	156
UNITED STATES | Leasing | Non Covered Loans
Financing Receivable, Impaired [Line Items]
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 [Line Items]
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 [Line Items]
Average Recorded Investment	6,208	2,572	5,446	2,632
Interest Income Recognized	0	0	0	0
UNITED STATES | Consumer | Personal | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	768	763	769	440
Interest Income Recognized	0	0	0	0
UNITED STATES | Consumer | Auto Loan | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	0	0	0	0
Interest Income Recognized	0	0	0	0
UNITED STATES | Consumer | Other | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	0	0	0	0
Interest Income Recognized	$ 0	$ 0	$ 0	$ 0