Segment Reporting (Operating Results and Total Assets Reportable Segments) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Assets	$ 31,654,874		$ 30,389,344
Net interest income	230,801	$ 241,551
Non-interest income	73,378	68,612
Non-interest expense	178,836	175,686
Pre-tax, pre-provision net revenue	125,343	134,477
Provision for credit losses	76,000	8,600
Income (loss) before income tax expense	49,343	125,877
Income tax expense	11,144	26,141
Net income	38,199	99,736
Operating Segments [Member] | Commercial Banking [Member]
Segment Reporting Information [Line Items]
Assets	12,332,819		11,541,803
Net interest income	99,316	98,342
Non-interest income	13,239	14,011
Non-interest expense	46,544	44,618
Pre-tax, pre-provision net revenue	66,011	67,735
Provision for credit losses	63,524	6,241
Income (loss) before income tax expense	2,487	61,494
Income tax expense	609	15,251
Net income	1,878	46,243
Operating Segments [Member] | HSA Bank [Member]
Segment Reporting Information [Line Items]
Assets	80,130		80,176
Net interest income	42,673	43,098
Non-interest income	26,383	25,577
Non-interest expense	37,078	33,522
Pre-tax, pre-provision net revenue	31,978	35,153
Provision for credit losses	0	0
Income (loss) before income tax expense	31,978	35,153
Income tax expense	8,538	9,316
Net income	23,440	25,837
Operating Segments [Member] | Community Banking [Member]
Segment Reporting Information [Line Items]
Assets	9,441,305		9,348,727
Net interest income	99,470	106,290
Non-interest income	27,620	25,382
Non-interest expense	98,967	95,075
Pre-tax, pre-provision net revenue	28,123	36,597
Provision for credit losses	12,561	2,359
Income (loss) before income tax expense	15,562	34,238
Income tax expense	3,081	7,258
Net income	12,481	26,980
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Assets	9,800,620		$ 9,418,638
Net interest income	(10,658)	(6,179)
Non-interest income	6,136	3,642
Non-interest expense	(3,753)	2,471
Pre-tax, pre-provision net revenue	(769)	(5,008)
Provision for credit losses	(85)	0
Income (loss) before income tax expense	(684)	(5,008)
Income tax expense	(1,084)	(5,684)
Net income	$ 400	$ 676