Segment Reporting (Operating Results and Total Assets Reportable Segments) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
Goodwill	$ 2,513,771	$ 538,373	$ 2,513,771	$ 538,373	$ 538,373	$ 538,373
Assets	69,052,566		69,052,566		34,915,599
Net interest income	551,003	229,691	1,431,911	674,307
Non-interest income	113,636	83,775	338,604	233,234
Non-interest expense	330,071	180,237	1,048,083	555,247
Pre-tax, pre-provision net revenue	334,568	133,229	722,432	352,294
Provision (benefit) for credit losses	36,531	7,750	237,619	(39,500)
Income (loss) before income taxes	298,037	125,479	484,813	391,794
Income tax expense	64,069	29,766	85,281	93,968
Net income	233,968	95,713	399,532	297,826
Operating Segments | Commercial Banking
Segment Reporting Information [Line Items]
Goodwill	1,865,887		1,865,887		131,000
Assets	40,907,410		40,907,410		15,398,159
Net interest income	333,554	152,012	954,044	434,087
Non-interest income	40,497	22,782	128,670	59,536
Non-interest expense	102,415	50,244	294,375	142,803
Pre-tax, pre-provision net revenue	271,636	124,550	788,339	350,820
Provision (benefit) for credit losses	33,341	5,099	238,054	(37,602)
Income (loss) before income taxes	238,295	119,451	550,285	388,422
Income tax expense	59,574	30,579	133,966	99,436
Net income	178,721	88,872	416,319	288,986
Operating Segments | HSA Bank
Segment Reporting Information [Line Items]
Goodwill	57,779		57,779		21,813
Assets	122,112		122,112		73,564
Net interest income	58,567	42,074	152,702	126,376
Non-interest income	25,842	24,756	79,352	78,315
Non-interest expense	36,725	32,374	110,674	100,802
Pre-tax, pre-provision net revenue	47,684	34,456	121,380	103,889
Provision (benefit) for credit losses	0	0	0	0
Income (loss) before income taxes	47,684	34,456	121,380	103,889
Income tax expense	12,779	9,199	32,530	27,738
Net income	34,905	25,257	88,850	76,151
Operating Segments | Consumer Banking
Segment Reporting Information [Line Items]
Goodwill	590,105		590,105		385,560
Assets	10,120,063		10,120,063		7,663,921
Net interest income	195,748	98,572	511,712	281,012
Non-interest income	33,842	24,292	92,541	71,262
Non-interest expense	109,588	73,212	312,464	222,672
Pre-tax, pre-provision net revenue	120,002	49,652	291,789	129,602
Provision (benefit) for credit losses	(1,989)	2,799	(5,906)	(1,833)
Income (loss) before income taxes	121,991	46,853	297,695	131,435
Income tax expense	31,718	11,151	77,352	31,282
Net income	90,273	35,702	220,343	100,153
Corporate, Non-Segment
Segment Reporting Information [Line Items]
Goodwill	0		0		0
Assets	17,902,981		17,902,981		$ 11,779,955
Net interest income	(36,866)	(62,967)	(186,547)	(167,168)
Non-interest income	13,455	11,945	38,041	24,121
Non-interest expense	81,343	24,407	330,570	88,970
Pre-tax, pre-provision net revenue	(104,754)	(75,429)	(479,076)	(232,017)
Provision (benefit) for credit losses	5,179	(148)	5,471	(65)
Income (loss) before income taxes	(109,933)	(75,281)	(484,547)	(231,952)
Income tax expense	(40,002)	(21,163)	(158,567)	(64,488)
Net income	$ (69,931)	$ (54,118)	$ (325,980)	$ (167,464)