Basis of Presentation and Informational Disclosures (Detail)	Mar. 31, 2015 item
Nature of Operations
Number of banking locations	161nwbi_NumberOfBankingLocations

Represents the number of banking locations in which the entity operates.

No definition available.

Name:	nwbi_NumberOfBankingLocations
Namespace Prefix:	nwbi_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant