SEGMENT INFORMATIO - Information about reportable segments (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Interest income	$ 147,995	$ 143,573	$ 440,597	$ 441,338
Net (charge) credit for transfer of funds	0	0	0	0
Interest expense	(25,163)	(25,395)	(71,312)	(78,284)
Net interest income	122,832	118,178	369,285	363,054
(Provision) release for loan and lease losses	(75,013)	(21,503)	(118,551)	(63,542)
Non-interest income (loss)	18,645	26,146	47,437	64,393
Direct non-interest expenses	(59,342)	(63,402)	(185,283)	(197,529)
Segment income	7,122	59,419	112,888	166,376
Average earnings assets	11,083,964	11,354,259	11,019,249	11,631,135
Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Interest income	32,317	34,605	99,361	104,865
Net (charge) credit for transfer of funds	(11,268)	(12,074)	(34,466)	(37,673)
Interest expense	0	0	0	0
Net interest income	21,049	22,531	64,895	67,192
(Provision) release for loan and lease losses	(20,495)	(3,860)	(40,598)	(21,608)
Non-interest income (loss)	2,908	5,222	11,258	14,381
Direct non-interest expenses	(8,174)	(8,864)	(27,675)	(29,828)
Segment income	(4,712)	15,029	7,880	30,137
Average earnings assets	2,434,963	2,549,358	2,469,037	2,576,194
Consumer Retail Banking [Member]
Segment Reporting Information [Line Items]
Interest income	43,769	44,455	130,055	135,655
Net (charge) credit for transfer of funds	9,351	2,810	20,799	10,546
Interest expense	(6,520)	(6,323)	(18,603)	(18,765)
Net interest income	46,600	40,942	132,251	127,436
(Provision) release for loan and lease losses	(33,067)	(8,655)	(47,976)	(24,451)
Non-interest income (loss)	11,242	11,292	37,224	35,318
Direct non-interest expenses	(27,193)	(27,100)	(82,677)	(87,218)
Segment income	(2,418)	16,479	38,822	51,085
Average earnings assets	1,758,653	1,973,424	1,771,376	1,989,426
Commercial And Corporate [Member]
Segment Reporting Information [Line Items]
Interest income	31,083	28,981	90,858	93,915
Net (charge) credit for transfer of funds	(8,748)	(6,700)	(27,071)	(18,212)
Interest expense	0	0	0	0
Net interest income	22,335	22,281	63,787	75,703
(Provision) release for loan and lease losses	(13,621)	(8,162)	(20,906)	(17,730)
Non-interest income (loss)	1,014	985	2,972	2,459
Direct non-interest expenses	(8,102)	(11,871)	(27,240)	(33,194)
Segment income	1,626	3,233	18,613	27,238
Average earnings assets	2,477,266	2,410,037	2,500,180	2,489,268
Treasury And Investments [Member]
Segment Reporting Information [Line Items]
Interest income	13,374	12,529	41,788	39,206
Net (charge) credit for transfer of funds	11,198	15,839	41,858	44,226
Interest expense	(12,924)	(14,487)	(36,842)	(45,828)
Net interest income	11,648	13,881	46,804	37,604
(Provision) release for loan and lease losses	0	0	0	0
Non-interest income (loss)	1,459	6,154	(10,273)	3,815
Direct non-interest expenses	(1,014)	(914)	(3,190)	(3,462)
Segment income	12,093	19,121	33,341	37,957
Average earnings assets	2,228,990	2,565,019	2,176,164	2,774,118
United States Operations [Member]
Segment Reporting Information [Line Items]
Interest income	18,446	13,944	50,910	40,091
Net (charge) credit for transfer of funds	(533)	125	(1,120)	1,113
Interest expense	(4,932)	(3,811)	(13,499)	(11,214)
Net interest income	12,981	10,258	36,291	29,990
(Provision) release for loan and lease losses	(789)	2,024	(885)	1,563
Non-interest income (loss)	697	884	1,776	2,799
Direct non-interest expenses	(7,605)	(7,556)	(23,579)	(23,070)
Segment income	5,284	5,610	13,603	11,282
Average earnings assets	1,581,726	1,252,271	1,492,727	1,188,463
Virgin Islands Operations [Member]
Segment Reporting Information [Line Items]
Interest income	9,006	9,059	27,625	27,606
Net (charge) credit for transfer of funds	0	0	0	0
Interest expense	(787)	(774)	(2,368)	(2,477)
Net interest income	8,219	8,285	25,257	25,129
(Provision) release for loan and lease losses	(7,041)	(2,850)	(8,186)	(1,316)
Non-interest income (loss)	1,325	1,609	4,480	5,621
Direct non-interest expenses	(7,254)	(7,097)	(20,922)	(20,757)
Segment income	(4,751)	(53)	629	8,677
Average earnings assets	$ 602,366	$ 604,150	$ 609,765	$ 613,666