Goodwill and Other Intangible Assets (Gross Carrying Value And Accumulated Amortization Of Other Intangible Assets) (Detail) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 538,373,000	$ 538,373,000
Gross Carrying Amount	47,625,000	43,000,000
Accumulated Amortization	(25,242,000)	(21,083,000)
Net Carrying Amount	22,383,000	21,917,000
Community Banking [Member]
Finite-Lived Intangible Assets [Line Items]
Goodwill	516,600,000
HSA Bank [Member]
Finite-Lived Intangible Assets [Line Items]
Goodwill	21,800,000
Core Deposits [Member] | HSA Bank [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	26,625,000	22,000,000
Accumulated Amortization	(15,618,000)	(13,073,000)
Net Carrying Amount	11,007,000	8,927,000
Customer Relationships [Member] | HSA Bank [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	21,000,000	21,000,000
Accumulated Amortization	(9,624,000)	(8,010,000)
Net Carrying Amount	$ 11,376,000	$ 12,990,000