Note Borrowings (Composition of federal funds purchased and assets sold under agreements to repurchase) (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Federal Funds Purchased and Securities Sold under Agreements to Repurchase
Assets sold under agreements to repurchase	$ 200,871	$ 281,529
Assets sold under agreements to repurchase	$ 200,871	$ 281,529

Amount, after the effects of master netting arrangements, of funds outstanding borrowed in the form of a security repurchase agreement between the entity and another party for the sale and repurchase of identical or substantially the same securities at a date certain for a specified price. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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Name:	us-gaap_SecuritiesSoldUnderAgreementsToRepurchase
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant