SEGMENT INFORMATION - Information about Reportable Segments (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Interest income	$ 624,967	$ 588,423	$ 585,292
Interest expense	(99,584)	(96,872)	(101,174)
Net interest income (loss)	525,383	491,551	484,118
(Provision) release for loan and lease losses	59,253	144,254	86,733
Non-interest income	82,310	62,387	87,954
Operating Segments [Member]
Segment Reporting Information [Line Items]
Interest income	624,967	588,423	585,292
Net (charge) credit for transfer of funds	0	0	0
Interest expense	(99,584)	(96,872)	(101,174)
Net interest income (loss)	525,383	491,551	484,118
(Provision) release for loan and lease losses	59,253	144,254	86,733
Non-interest income	82,310	62,387	87,954
Direct non-interest expenses	(250,255)	(242,277)	(253,954)
Segment income	298,185	167,407	231,385
Average earnings assets	11,265,470	11,035,328	11,466,576
Mortgage Banking Segment [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)	79,389
Non-interest income	17,073
Mortgage Banking Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Interest income	127,042	131,718	138,955
Net (charge) credit for transfer of funds	(47,653)	(45,759)	(49,435)
Interest expense	0	0	0
Net interest income (loss)	79,389	85,959	89,520
(Provision) release for loan and lease losses	13,083	47,713	24,873
Non-interest income	17,073	12,825	19,531
Direct non-interest expenses	(38,213)	(36,403)	(38,170)
Segment income	45,166	14,668	46,008
Average earnings assets	2,258,974	2,451,655	2,562,245
Consumer Retail Banking Segment [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)	217,933
Non-interest income	47,706
Consumer Retail Banking Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Interest income	181,166	173,690	179,485
Net (charge) credit for transfer of funds	65,092	27,475	13,996
Interest expense	(28,325)	(25,240)	(24,787)
Net interest income (loss)	217,933	175,925	168,694
(Provision) release for loan and lease losses	23,516	53,778	34,246
Non-interest income	47,706	43,924	44,535
Direct non-interest expenses	(112,176)	(108,165)	(112,787)
Segment income	129,947	57,906	66,196
Average earnings assets	1,636,002	1,749,148	1,951,214
Commercial And Corporate Segment [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)	78,675
Non-interest income	5,158
Commercial And Corporate Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Interest income	138,706	128,871	123,084
Net (charge) credit for transfer of funds	(60,031)	(36,904)	(26,364)
Interest expense	0	0	0
Net interest income (loss)	78,675	91,967	96,720
(Provision) release for loan and lease losses	4,804	33,296	28,578
Non-interest income	5,158	7,176	7,811
Direct non-interest expenses	(32,371)	(35,142)	(40,676)
Segment income	46,658	30,705	35,277
Average earnings assets	2,530,635	2,489,948	2,497,037
Treasury And Investments Segment [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)	61,628
Non-interest income	2,505
Treasury And Investments Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Interest income	61,913	48,071	50,372
Net (charge) credit for transfer of funds	44,540	56,865	60,787
Interest expense	(44,825)	(49,577)	(57,924)
Net interest income (loss)	61,628	55,359	53,235
(Provision) release for loan and lease losses	0	0	0
Non-interest income	2,505	(10,206)	5,423
Direct non-interest expenses	(2,966)	(3,376)	(4,047)
Segment income	61,167	41,777	54,611
Average earnings assets	2,552,130	2,215,551	2,616,877
United States Operations Segment [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)	59,056
Non-interest income	3,020
United States Operations Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Interest income	83,971	69,760	56,037
Net (charge) credit for transfer of funds	(1,948)	(1,677)	1,016
Interest expense	(22,967)	(18,902)	(15,240)
Net interest income (loss)	59,056	49,181	41,813
(Provision) release for loan and lease losses	11,882	3,644	(1,369)
Non-interest income	3,020	2,664	3,554
Direct non-interest expenses	(33,566)	(32,197)	(30,678)
Segment income	16,628	16,004	16,058
Average earnings assets	1,750,155	1,525,191	1,226,633
Virgin Islands Operations Segment [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)	28,702
Non-interest income	6,848
Virgin Islands Operations Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Interest income	32,169	36,313	37,359
Net (charge) credit for transfer of funds	0	0	0
Interest expense	(3,467)	(3,153)	(3,223)
Net interest income (loss)	28,702	33,160	34,136
(Provision) release for loan and lease losses	5,968	5,823	405
Non-interest income	6,848	6,004	7,100
Direct non-interest expenses	(30,963)	(26,994)	(27,596)
Segment income	(1,381)	6,347	13,235
Average earnings assets	$ 537,574	$ 603,835	$ 612,570