Shareholders' Equity (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Shareholders' Equity
Bad debt deductions for which no deferred income taxes have been provided	$ 39.1	$ 39.1

Cumulative amount of bad debt deductions net of losses absorbed included in retained earnings as of the balance sheet date for which no deferred income taxes have been provided based on the Internal Revenue Code (IRC) rules.

No definition available.

Name:	nwbi_BadDebtDeductionForWhichNoDeferredTaxesHaveBeenProvided
Namespace Prefix:	nwbi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant