Note Allowance for loan losses (Disclosures related to loans individually evaluated for impairment) (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable, Impaired [Line Items]
Related Allowance	$ 115,191	$ 111,377
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	112,412	129,350
Impaired Financing Receivable, with Related Allowance, Recorded Investment	842,375	826,707
Recorded Investment	954,787	956,057
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	170,879	182,772
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	966,536	908,563
Unpaid Principal Balance	1,137,415	1,091,335
PUERTO RICO
Financing Receivable, Impaired [Line Items]
Related Allowance	112,172	108,523
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	109,083	126,476
Impaired Financing Receivable, with Related Allowance, Recorded Investment	833,171	817,866
Recorded Investment	942,254	944,342
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	166,613	179,009
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	955,541	898,124
Unpaid Principal Balance	1,122,154	1,077,133
UNITED STATES | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Related Allowance	3,019	2,854
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	3,329	2,874
Impaired Financing Receivable, with Related Allowance, Recorded Investment	9,204	8,841
Recorded Investment	12,533	11,715
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	4,266	3,763
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	10,995	10,439
Unpaid Principal Balance	15,261	14,202
Commercial multi-family | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Related Allowance	30	34
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	0	0
Impaired Financing Receivable, with Related Allowance, Recorded Investment	204	82
Recorded Investment	204	82
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	0	0
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	204	82
Unpaid Principal Balance	204	82
Commercial multi-family | PUERTO RICO | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Related Allowance	30	34
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	0	0
Impaired Financing Receivable, with Related Allowance, Recorded Investment	204	82
Recorded Investment	204	82
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	0	0
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	204	82
Unpaid Principal Balance	204	82
CRE non-owner occupied | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Related Allowance	25,535	24,537
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	7,617	15,935
Impaired Financing Receivable, with Related Allowance, Recorded Investment	109,814	104,119
Recorded Investment	117,431	120,054
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	12,780	29,631
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	120,252	105,047
Unpaid Principal Balance	133,032	134,678
CRE non-owner occupied | PUERTO RICO | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Related Allowance	25,535	24,537
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	7,617	15,935
Impaired Financing Receivable, with Related Allowance, Recorded Investment	109,814	104,119
Recorded Investment	117,431	120,054
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	12,780	29,631
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	120,252	105,047
Unpaid Principal Balance	133,032	134,678
CRE owner occupied | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Related Allowance	8,729	13,007
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	28,389	31,962
Impaired Financing Receivable, with Related Allowance, Recorded Investment	120,196	131,634
Recorded Investment	148,585	163,596
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	59,034	50,094
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	178,892	169,013
Unpaid Principal Balance	237,926	219,107
CRE owner occupied | PUERTO RICO | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Related Allowance	8,729	13,007
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	28,389	31,962
Impaired Financing Receivable, with Related Allowance, Recorded Investment	120,196	131,634
Recorded Investment	148,585	163,596
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	59,034	50,094
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	178,892	169,013
Unpaid Principal Balance	237,926	219,107
Commercial and industrial | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Related Allowance	6,569	4,797
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	15,677	7,828
Impaired Financing Receivable, with Related Allowance, Recorded Investment	46,807	46,862
Recorded Investment	62,484	54,690
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	25,105	11,478
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	49,869	49,301
Unpaid Principal Balance	74,974	60,779
Commercial and industrial | PUERTO RICO | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Related Allowance	6,569	4,797
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	15,677	7,828
Impaired Financing Receivable, with Related Allowance, Recorded Investment	46,807	46,862
Recorded Investment	62,484	54,690
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	25,105	11,478
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	49,869	49,301
Unpaid Principal Balance	74,974	60,779
Mortgages | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Related Allowance	51,421	44,610
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	59,993	73,246
Impaired Financing Receivable, with Related Allowance, Recorded Investment	459,235	433,118
Recorded Investment	519,228	506,364
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	73,207	91,175
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	511,190	474,220
Unpaid Principal Balance	584,397	565,395
Mortgages | PUERTO RICO | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Related Allowance	49,129	42,428
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	57,400	70,751
Impaired Financing Receivable, with Related Allowance, Recorded Investment	452,734	426,737
Recorded Investment	510,134	497,488
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	69,694	87,806
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	502,908	466,249
Unpaid Principal Balance	572,602	554,055
Mortgages | UNITED STATES | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Related Allowance	2,292	2,182
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	2,593	2,495
Impaired Financing Receivable, with Related Allowance, Recorded Investment	6,501	6,381
Recorded Investment	9,094	8,876
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	3,513	3,369
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	8,282	7,971
Unpaid Principal Balance	11,795	11,340
Leasing | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Related Allowance	450	535
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	0	0
Impaired Financing Receivable, with Related Allowance, Recorded Investment	1,468	1,817
Recorded Investment	1,468	1,817
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	0	0
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	1,468	1,817
Unpaid Principal Balance	1,468	1,817
Leasing | PUERTO RICO | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Related Allowance	450	535
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	0	0
Impaired Financing Receivable, with Related Allowance, Recorded Investment	1,468	1,817
Recorded Investment	1,468	1,817
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	0	0
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	1,468	1,817
Unpaid Principal Balance	1,468	1,817
Consumer | Credit cards | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Related Allowance	5,500	5,588
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	0	0
Impaired Financing Receivable, with Related Allowance, Recorded Investment	35,782	37,464
Recorded Investment	35,782	37,464
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	0	0
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	35,782	37,464
Unpaid Principal Balance	35,782	37,464
Consumer | Credit cards | PUERTO RICO | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Related Allowance	5,500	5,588
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	0	0
Impaired Financing Receivable, with Related Allowance, Recorded Investment	35,782	37,464
Recorded Investment	35,782	37,464
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	0	0
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	35,782	37,464
Unpaid Principal Balance	35,782	37,464
Consumer | Home equity lines of credit | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Related Allowance	501	667
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	519	300
Impaired Financing Receivable, with Related Allowance, Recorded Investment	2,149	2,421
Recorded Investment	2,668	2,721
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	536	315
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	2,158	2,429
Unpaid Principal Balance	2,694	2,744
Consumer | Home equity lines of credit | UNITED STATES | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Related Allowance	501	667
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	519	300
Impaired Financing Receivable, with Related Allowance, Recorded Investment	2,149	2,421
Recorded Investment	2,668	2,721
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	536	315
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	2,158	2,429
Unpaid Principal Balance	2,694	2,744
Consumer | Personal | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Related Allowance	15,842	16,960
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	217	79
Impaired Financing Receivable, with Related Allowance, Recorded Investment	63,569	66,082
Recorded Investment	63,786	66,161
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	217	79
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	63,570	66,082
Unpaid Principal Balance	63,787	66,161
Consumer | Personal | PUERTO RICO | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Related Allowance	15,616	16,955
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	0	0
Impaired Financing Receivable, with Related Allowance, Recorded Investment	63,015	66,043
Recorded Investment	63,015	66,043
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	0	0
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	63,015	66,043
Unpaid Principal Balance	63,015	66,043
Consumer | Personal | UNITED STATES | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Related Allowance	226	5
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	217	79
Impaired Financing Receivable, with Related Allowance, Recorded Investment	554	39
Recorded Investment	771	118
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	217	79
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	555	39
Unpaid Principal Balance	772	118
Consumer | Auto | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Related Allowance	440	474
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	0	0
Impaired Financing Receivable, with Related Allowance, Recorded Investment	2,049	2,117
Recorded Investment	2,049	2,117
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	0	0
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	2,049	2,117
Unpaid Principal Balance	2,049	2,117
Consumer | Auto | PUERTO RICO | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Related Allowance	440	474
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	0	0
Impaired Financing Receivable, with Related Allowance, Recorded Investment	2,049	2,117
Recorded Investment	2,049	2,117
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	0	0
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	2,049	2,117
Unpaid Principal Balance	2,049	2,117
Consumer | Other | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Related Allowance	174	168
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	0	0
Impaired Financing Receivable, with Related Allowance, Recorded Investment	1,102	991
Recorded Investment	1,102	991
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	0	0
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	1,102	991
Unpaid Principal Balance	1,102	991
Consumer | Other | PUERTO RICO | Non Covered Loans
Financing Receivable, Impaired [Line Items]
Related Allowance	174	168
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	0	0
Impaired Financing Receivable, with Related Allowance, Recorded Investment	1,102	991
Recorded Investment	1,102	991
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	0	0
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	1,102	991
Unpaid Principal Balance	$ 1,102	$ 991