SEGMENT INFORMATIO - Information about reportable segments (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Interest Income	$ 170,402	$ 172,295	$ 494,282	$ 508,277
Interest expense	(21,706)	(27,870)	(71,727)	(81,125)
Net interest income	148,696	144,425	422,555	427,152
(Provision) release for credit losses	(46,914)	(7,398)	(163,294)	(31,340)
Non-interest income (loss)	29,934	21,401	81,026	66,167
Commercial And Corporate Segment [Member]
Segment Reporting Information [Line Items]
Net interest income	35,803	25,699	86,631	69,171
Non-interest income (loss)	2,838	2,331	7,673	7,146
Treasury And Investments Segment [Member]
Segment Reporting Information [Line Items]
Net interest income	18,577	18,147	55,549	52,804
Non-interest income (loss)	5,457	(433)	13,777	(287)
United States Operations Segment [Member]
Segment Reporting Information [Line Items]
Net interest income	12,918	14,977	39,939	47,328
Non-interest income (loss)	1,058	640	2,534	1,942
Virgin Islands Operations Segment [Member]
Segment Reporting Information [Line Items]
Net interest income	6,409	6,447	19,650	19,884
Non-interest income (loss)	1,510	1,758	5,565	5,873
Operating Segments [Member]
Segment Reporting Information [Line Items]
Interest Income	170,402	172,295	494,282	508,277
Net (charge) credit for transfer of funds	0	0	0	0
Interest expense	(21,706)	(27,870)	(71,727)	(81,125)
Net interest income	148,696	144,425	422,555	427,152
(Provision) release for credit losses	(46,914)	(7,398)	(163,294)	(31,340)
Non-interest income (loss)	29,934	21,401	81,026	66,167
Direct non-interest expenses	(62,280)	(62,647)	(181,318)	(190,974)
Segment income	69,436	95,781	158,969	271,005
Average earnings assets	14,758,254	11,553,259	13,079,032	11,442,243
Operating Segments [Member] | Mortgage Banking Segment [Member]
Segment Reporting Information [Line Items]
Interest Income	32,293	30,091	89,353	91,493
Net (charge) credit for transfer of funds	(11,627)	(13,100)	(34,176)	(39,442)
Interest expense	0	0	0	0
Net interest income	20,666	16,991	55,177	52,051
(Provision) release for credit losses	(11,614)	(2,134)	(29,491)	(9,241)
Non-interest income (loss)	6,756	4,400	14,843	12,255
Direct non-interest expenses	(7,659)	(7,768)	(22,647)	(25,810)
Segment income	8,149	11,489	17,882	29,255
Average earnings assets	2,243,345	2,141,383	2,076,419	2,182,680
Operating Segments [Member] | Consumer Reatail Banking Segment [Member]
Segment Reporting Information [Line Items]
Interest Income	60,157	55,772	174,848	158,548
Net (charge) credit for transfer of funds	3,514	16,557	19,485	54,743
Interest expense	(9,348)	(10,165)	(28,724)	(27,377)
Net interest income	54,323	62,164	165,609	185,914
(Provision) release for credit losses	(12,404)	(11,187)	(56,254)	(28,982)
Non-interest income (loss)	12,315	12,705	36,634	39,238
Direct non-interest expenses	(32,035)	(30,282)	(89,659)	(88,533)
Segment income	22,199	33,400	56,330	107,637
Average earnings assets	2,197,601	2,009,060	2,141,329	1,914,372
Operating Segments [Member] | Commercial And Corporate Segment [Member]
Segment Reporting Information [Line Items]
Interest Income	37,571	39,146	102,225	114,643
Net (charge) credit for transfer of funds	(1,768)	(13,447)	(15,594)	(45,472)
Interest expense	0	0	0	0
Net interest income	35,803	25,699	86,631	69,171
(Provision) release for credit losses	(19,139)	5,677	(51,844)	12,665
Non-interest income (loss)	2,838	2,331	7,673	7,146
Direct non-interest expenses	(6,251)	(8,256)	(19,688)	(26,869)
Segment income	13,251	25,451	22,772	62,113
Average earnings assets	3,064,272	2,487,409	2,684,803	2,509,611
Operating Segments [Member] | Treasury And Investments Segment [Member]
Segment Reporting Information [Line Items]
Interest Income	12,572	15,671	41,631	47,553
Net (charge) credit for transfer of funds	11,972	11,411	34,441	34,403
Interest expense	(5,967)	(8,935)	(20,523)	(29,152)
Net interest income	18,577	18,147	55,549	52,804
(Provision) release for credit losses	0	0	(2,765)	0
Non-interest income (loss)	5,457	(433)	13,777	(287)
Direct non-interest expenses	(717)	(740)	(2,133)	(2,031)
Segment income	23,317	16,974	64,428	50,486
Average earnings assets	4,725,125	2,485,141	3,690,782	2,429,576
Operating Segments [Member] | United States Operations Segment [Member]
Segment Reporting Information [Line Items]
Interest Income	20,427	24,229	63,754	73,350
Net (charge) credit for transfer of funds	(2,091)	(1,421)	(4,156)	(4,232)
Interest expense	(5,418)	(7,831)	(19,659)	(21,790)
Net interest income	12,918	14,977	39,939	47,328
(Provision) release for credit losses	(1,679)	(1,462)	(15,944)	(7,764)
Non-interest income (loss)	1,058	640	2,534	1,942
Direct non-interest expenses	(8,387)	(8,496)	(25,221)	(25,641)
Segment income	3,910	5,659	1,308	15,865
Average earnings assets	2,061,596	1,963,559	2,025,482	1,935,768
Operating Segments [Member] | Virgin Islands Operations Segment [Member]
Segment Reporting Information [Line Items]
Interest Income	7,382	7,386	22,471	22,690
Net (charge) credit for transfer of funds	0	0	0	0
Interest expense	(973)	(939)	(2,821)	(2,806)
Net interest income	6,409	6,447	19,650	19,884
(Provision) release for credit losses	(2,078)	1,708	(6,996)	1,982
Non-interest income (loss)	1,510	1,758	5,565	5,873
Direct non-interest expenses	(7,231)	(7,105)	(21,970)	(22,090)
Segment income	(1,390)	2,808	(3,751)	5,649
Average earnings assets	$ 466,315	$ 466,707	$ 460,217	$ 470,236