SEGMENT INFORMATION - Information about reportable segments (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Interest Income	$ 166,472	$ 149,418
Interest expense	(26,291)	(24,725)
Net interest income	140,181	124,693
(Provision) releases for loan and lease losses	(11,820)	(20,544)
Non-interest income	22,543	22,784
Commercial And Corporate Banking Segment [Member]
Segment Reporting Information [Line Items]
Net interest income	20,933	18,920
Non-interest income	2,518	1,259
Treasury And Investments Segment [Member]
Segment Reporting Information [Line Items]
Net interest income	16,795	12,518
Non-interest income	74	2,378
United States Operations Segment [Member]
Segment Reporting Information [Line Items]
Net interest income	16,209	13,392
Non-interest income	533	1,408
Virgin Islands Operations Segment [Member]
Segment Reporting Information [Line Items]
Net interest income	6,961	7,609
Non-interest income	1,805	1,725
Operating Segments [Member]
Segment Reporting Information [Line Items]
Interest Income	166,472	149,418
Net (charge) credit for transfer of funds	0	0
Interest expense	(26,291)	(24,725)
Net interest income	140,181	124,693
(Provision) releases for loan and lease losses	(11,820)	(20,544)
Non-interest income	22,543	22,784
Direct non-interest expenses	(63,699)	(57,861)
Segment income (loss)	87,205	69,072
Average earnings assets	11,280,192	11,244,444
Operating Segments [Member] | Mortgage Banking Segment [Member]
Segment Reporting Information [Line Items]
Interest Income	30,857	32,321
Net (charge) credit for transfer of funds	(13,108)	(11,116)
Interest expense	0	0
Net interest income	17,749	21,205
(Provision) releases for loan and lease losses	(6,412)	(381)
Non-interest income	3,606	4,084
Direct non-interest expenses	(8,481)	(7,720)
Segment income (loss)	6,462	17,188
Average earnings assets	2,188,093	2,293,482
Operating Segments [Member] | Consumer (Retail) Banking Segment [Member]
Segment Reporting Information [Line Items]
Interest Income	49,975	42,550
Net (charge) credit for transfer of funds	19,662	15,222
Interest expense	(8,103)	(6,723)
Net interest income	61,534	51,049
(Provision) releases for loan and lease losses	(9,412)	(5,793)
Non-interest income	14,007	11,930
Direct non-interest expenses	(29,404)	(26,901)
Segment income (loss)	36,725	30,285
Average earnings assets	1,824,240	1,566,795
Operating Segments [Member] | Commercial And Corporate Banking Segment [Member]
Segment Reporting Information [Line Items]
Interest Income	37,387	32,337
Net (charge) credit for transfer of funds	(16,454)	(13,417)
Interest expense	0	0
Net interest income	20,933	18,920
(Provision) releases for loan and lease losses	8,050	(6,800)
Non-interest income	2,518	1,259
Direct non-interest expenses	(8,989)	(6,714)
Segment income (loss)	22,512	6,665
Average earnings assets	2,499,709	2,632,220
Operating Segments [Member] | Treasury And Investments Segment [Member]
Segment Reporting Information [Line Items]
Interest Income	16,249	14,254
Net (charge) credit for transfer of funds	11,250	9,974
Interest expense	(10,704)	(11,710)
Net interest income	16,795	12,518
(Provision) releases for loan and lease losses	0	0
Non-interest income	74	2,378
Direct non-interest expenses	(723)	(948)
Segment income (loss)	16,146	13,948
Average earnings assets	2,392,467	2,470,830
Operating Segments [Member] | United States Operations Segment [Member]
Segment Reporting Information [Line Items]
Interest Income	24,157	19,527
Net (charge) credit for transfer of funds	(1,350)	(663)
Interest expense	(6,598)	(5,472)
Net interest income	16,209	13,392
(Provision) releases for loan and lease losses	(4,364)	(1,459)
Non-interest income	533	1,408
Direct non-interest expenses	(8,362)	(7,956)
Segment income (loss)	4,016	5,385
Average earnings assets	1,902,771	1,709,918
Operating Segments [Member] | Virgin Islands Operations Segment [Member]
Segment Reporting Information [Line Items]
Interest Income	7,847	8,429
Net (charge) credit for transfer of funds	0	0
Interest expense	(886)	(820)
Net interest income	6,961	7,609
(Provision) releases for loan and lease losses	318	(6,111)
Non-interest income	1,805	1,725
Direct non-interest expenses	(7,740)	(7,622)
Segment income (loss)	1,344	(4,399)
Average earnings assets	$ 472,912	$ 571,199