Segment Reporting (Operating Results and Total Assets Reportable Segments) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
Goodwill	$ 2,513,771	$ 538,373	$ 538,373	$ 538,373
Assets	65,131,484		34,915,599
Net interest income	394,248	223,764
Non-interest income	104,035	76,757
Non-interest expense	359,785	187,982
Pre-tax, pre-provision net revenue	138,498	112,539
Provision (benefit) for credit losses	188,845	(25,750)
Income (loss) before income taxes	(50,347)	138,289
Income tax (benefit) expense	(33,600)	30,211
Net (loss) income	(16,747)	108,078
Operating Segments | Commercial Banking
Segment Reporting Information [Line Items]
Goodwill	1,865,887		131,000
Assets	39,028,843		15,398,159
Net interest income	287,069	141,486
Non-interest income	38,743	18,376
Non-interest expense	89,240	46,284
Pre-tax, pre-provision net revenue	236,572	113,578
Provision (benefit) for credit losses	181,931	(19,373)
Income (loss) before income taxes	54,641	132,951
Income tax (benefit) expense	10,055	34,035
Net (loss) income	44,586	98,916
Operating Segments | HSA Bank
Segment Reporting Information [Line Items]
Goodwill	57,779		21,813
Assets	132,266		73,564
Net interest income	44,577	42,109
Non-interest income	26,958	27,005
Non-interest expense	36,409	36,005
Pre-tax, pre-provision net revenue	35,126	33,109
Provision (benefit) for credit losses	0	0
Income (loss) before income taxes	35,126	33,109
Income tax (benefit) expense	9,414	8,840
Net (loss) income	25,712	24,269
Operating Segments | Consumer Banking
Segment Reporting Information [Line Items]
Goodwill	590,105		385,560
Assets	9,587,880		7,663,921
Net interest income	136,580	89,365
Non-interest income	27,892	22,872
Non-interest expense	95,747	75,311
Pre-tax, pre-provision net revenue	68,725	36,926
Provision (benefit) for credit losses	7,136	(6,386)
Income (loss) before income taxes	61,589	43,312
Income tax (benefit) expense	15,964	10,308
Net (loss) income	45,625	33,004
Corporate, Non-Segment
Segment Reporting Information [Line Items]
Goodwill	0		0
Assets	16,382,495		$ 11,779,955
Net interest income	(73,978)	(49,196)
Non-interest income	10,442	8,504
Non-interest expense	138,389	30,382
Pre-tax, pre-provision net revenue	(201,925)	(71,074)
Provision (benefit) for credit losses	(222)	9
Income (loss) before income taxes	(201,703)	(71,083)
Income tax (benefit) expense	(69,033)	(22,972)
Net (loss) income	$ (132,670)	$ (48,111)