CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
CONSOLIDATED STATEMENTS OF CASH FLOWS
Interest on deposits and borrowings, interest credited to deposit accounts	$ 5,256nwbi_CashPaidForInterestOnDeposits	$ 5,819nwbi_CashPaidForInterestOnDeposits

This element represents interest paid to depositors on deposit accounts held by the institution.

No definition available.

Name:	nwbi_CashPaidForInterestOnDeposits
Namespace Prefix:	nwbi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration