Segment Reporting (Operating Results and Total Assets Reportable Segments) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Total Assets	$ 34,915,599	$ 32,590,690
Net interest income (expense)	901,089	891,393	$ 955,127
Noninterest Income	323,372	285,277	285,315
Non-interest expense	745,100	758,946	715,950
Pre-tax, pre-provision net revenue	479,361	417,724	524,492
(Benefit) provision for credit losses	(54,500)	137,750	37,800
Income (loss) before income tax expense	533,861	279,974	486,692
Income tax expense	124,997	59,353	103,969
Net income	408,864	220,621	382,723
Goodwill	538,373	538,373
Operating Segments [Member] | Commercial Banking [Member]
Segment Reporting Information [Line Items]
Total Assets	15,400,886	14,732,792
Net interest income (expense)	587,485	515,027	476,779
Noninterest Income	112,270	90,498	91,184
Non-interest expense	257,461	260,953	252,485
Pre-tax, pre-provision net revenue	442,294	344,572	315,478
(Benefit) provision for credit losses	(51,348)	152,571	29,714
Income (loss) before income tax expense	493,642	192,001	285,764
Income tax expense	124,891	46,848	70,298
Net income	368,751	145,153	215,466
Goodwill	131,000	131,000
Operating Segments [Member] | HSA Bank [Member]
Segment Reporting Information [Line Items]
Total Assets	73,564	80,352
Net interest income (expense)	168,595	162,363	172,685
Noninterest Income	102,814	100,826	97,041
Non-interest expense	135,997	140,637	135,586
Pre-tax, pre-provision net revenue	135,412	122,552	134,140
(Benefit) provision for credit losses	0	0	0
Income (loss) before income tax expense	135,412	122,552	134,140
Income tax expense	36,155	32,721	35,547
Net income	99,257	89,831	98,593
Goodwill	21,813	21,813
Operating Segments [Member] | Community Banking [Member]
Segment Reporting Information [Line Items]
Total Assets	7,663,218	7,726,287
Net interest income (expense)	373,130	331,821	347,377
Noninterest Income	67,155	74,147	77,149
Non-interest expense	296,260	317,215	317,494
Pre-tax, pre-provision net revenue	144,025	88,753	107,032
(Benefit) provision for credit losses	(3,068)	(14,722)	8,086
Income (loss) before income tax expense	147,093	103,475	98,946
Income tax expense	32,361	22,558	20,581
Net income	114,732	80,917	78,365
Goodwill	385,560	385,560
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Total Assets	11,777,931	10,051,259
Net interest income (expense)	(228,121)	(117,818)	(41,714)
Noninterest Income	41,133	19,806	19,941
Non-interest expense	55,382	40,141	10,385
Pre-tax, pre-provision net revenue	(242,370)	(138,153)	(32,158)
(Benefit) provision for credit losses	(84)	(99)	0
Income (loss) before income tax expense	(242,286)	(138,054)	(32,158)
Income tax expense	(68,410)	(42,774)	(22,457)
Net income	(173,876)	(95,280)	$ (9,701)
Goodwill	$ 0	$ 0