Goodwill and Other Intangible Assets (Gross Carrying Value And Accumulated Amortization Of Other Intangible Assets) (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 43,000	$ 43,000
Accumulated Amortization	(12,411)	(9,326)
Net Carrying Amount	30,589	33,674
Goodwill	538,373	538,373
HSA Bank [Member]
Finite-Lived Intangible Assets [Line Items]
Goodwill	21,813	21,813
Community Banking [Member]
Finite-Lived Intangible Assets [Line Items]
Goodwill	516,560	516,560
Core Deposits [Member] | HSA Bank [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	22,000	22,000
Accumulated Amortization	(8,036)	(6,162)
Net Carrying Amount	13,964	15,838
Customer Relationships [Member] | HSA Bank [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	21,000	21,000
Accumulated Amortization	(4,375)	(3,164)
Net Carrying Amount	$ 16,625	$ 17,836