SEGMENT INFORMATION - Information about Reportable Segments (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Interest income	$ 692,982	$ 675,897	$ 624,967
Interest expense	(92,660)	(108,816)	(99,584)
Net interest income (loss)	600,322	567,081	525,383
Provision (release)	168,717	40,225	59,253
Non-interest income	111,226	90,572	82,310
Operating Segments [Member]
Segment Reporting Information [Line Items]
Interest income	692,982	675,897	624,967
Net (charge) credit for transfer of funds	0	0	0
Interest expense	(92,660)	(108,816)	(99,584)
Net interest income (loss)	600,322	567,081	525,383
Provision (release)	170,985	39,813	58,989
Non-interest income	111,226	90,572	82,310
Direct non-interest expenses	(258,864)	(252,603)	(250,519)
Segment income	281,699	365,237	298,185
Average earnings assets	14,201,505	11,497,408	11,265,470
Mortgage Banking Segment [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)	76,025	68,803	79,389
Non-interest income	22,069	16,825	17,073
Mortgage Banking Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Interest income	128,043	120,981	127,042
Net (charge) credit for transfer of funds	(52,018)	(52,178)	(47,653)
Interest expense	0	0	0
Net interest income (loss)	76,025	68,803	79,389
Provision (release)	22,518	13,499	13,083
Non-interest income	22,069	16,825	17,073
Direct non-interest expenses	(33,054)	(34,825)	(38,213)
Segment income	42,522	37,304	45,166
Average earnings assets	2,241,753	2,161,772	2,258,974
Consumer Retail Banking Segment [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)	220,678	244,535	217,933
Non-interest income	50,962	51,729	47,706
Consumer Retail Banking Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Interest income	240,725	216,066	181,166
Net (charge) credit for transfer of funds	18,771	66,675	65,092
Interest expense	(38,818)	(38,206)	(28,325)
Net interest income (loss)	220,678	244,535	217,933
Provision (release)	54,094	41,043	23,516
Non-interest income	50,962	51,729	47,706
Direct non-interest expenses	(131,133)	(116,854)	(112,176)
Segment income	86,413	138,367	129,947
Average earnings assets	2,202,595	1,960,352	1,636,002
Commercial And Corporate Segment [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)	135,591	91,266	78,675
Non-interest income	12,606	11,714	5,158
Commercial And Corporate Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Interest income	155,254	148,224	138,706
Net (charge) credit for transfer of funds	(19,663)	(56,958)	(60,031)
Interest expense	0	0	0
Net interest income (loss)	135,591	91,266	78,675
Provision (release)	74,607	(17,977)	4,540
Non-interest income	12,606	11,714	5,158
Direct non-interest expenses	(28,631)	(35,130)	(32,635)
Segment income	44,959	85,827	46,658
Average earnings assets	3,039,786	2,489,933	2,530,635
Treasury And Investments Segment [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)	87,879	73,626	61,628
Non-interest income	13,708	(225)	2,505
Treasury And Investments Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Interest income	55,003	63,175	61,913
Net (charge) credit for transfer of funds	59,074	47,477	44,540
Interest expense	(26,198)	(37,026)	(44,825)
Net interest income (loss)	87,879	73,626	61,628
Provision (release)	2,774	0	0
Non-interest income	13,708	(225)	2,505
Direct non-interest expenses	(3,449)	(2,729)	(2,966)
Segment income	95,364	70,672	61,167
Average earnings assets	4,232,144	2,487,084	2,552,130
United States Operations Segment [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)	54,025	62,539	59,056
Non-interest income	4,630	2,807	3,020
United States Operations Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Interest income	84,169	97,406	83,971
Net (charge) credit for transfer of funds	(6,164)	(5,016)	(1,948)
Interest expense	(23,980)	(29,851)	(22,967)
Net interest income (loss)	54,025	62,539	59,056
Provision (release)	12,592	7,296	11,882
Non-interest income	4,630	2,807	3,020
Direct non-interest expenses	(33,782)	(34,070)	(33,566)
Segment income	12,281	23,980	16,628
Average earnings assets	2,026,619	1,931,015	1,750,155
Virgin Islands Operations Segment [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)	26,124	26,312	28,702
Non-interest income	7,251	7,722	6,848
Virgin Islands Operations Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Interest income	29,788	30,045	32,169
Net (charge) credit for transfer of funds	0	0	0
Interest expense	(3,664)	(3,733)	(3,467)
Net interest income (loss)	26,124	26,312	28,702
Provision (release)	4,400	(4,048)	5,968
Non-interest income	7,251	7,722	6,848
Direct non-interest expenses	(28,815)	(28,995)	(30,963)
Segment income	160	9,087	(1,381)
Average earnings assets	$ 458,608	$ 467,252	$ 537,574