Goodwill and Other Intangible Assets - Carrying Amount of Goodwill (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2015
Goodwill [Line Items]
Goodwill	$ 690,637	$ 690,637	$ 686,339
Goodwill from business combinations	4,298
Wealth Management
Goodwill [Line Items]
Goodwill	21,218	21,218	20,517
Goodwill from business combinations	701
Consumer Lending
Goodwill [Line Items]
Goodwill	200,103	200,103	199,119
Goodwill from business combinations	984
Commercial Lending
Goodwill [Line Items]
Goodwill	316,258	316,258	314,260
Goodwill from business combinations	1,998
Investment Management
Goodwill [Line Items]
Goodwill	153,058	$ 153,058	$ 152,443
Goodwill from business combinations	$ 615