Loans Receivable and Allowance for Loan Losses (Details 10) (USD $)	12 Months Ended
Dec. 31, 2013	Dec. 31, 2012
Financial instruments with off-balance-sheet risk
Financial instruments with off-balance-sheet risk	$ 634,679,000	$ 525,780,000
Recourse provisions for recovery of amounts from third parties	0	0
Loan commitments
Financial instruments with off-balance-sheet risk
Financial instruments with off-balance-sheet risk	174,998,000	66,973,000
Outstanding loan commitments for fixed rate loans	55,100,000
Outstanding loan commitments for adjustable rate loans	119,900,000
Undisbursed lines of credit
Financial instruments with off-balance-sheet risk
Financial instruments with off-balance-sheet risk	432,334,000	401,685,000
Standby letters of credit
Financial instruments with off-balance-sheet risk
Financial instruments with off-balance-sheet risk	27,347,000	57,122,000
Maximum potential amount of future payments	27,300,000
Maximum potential amount of future payments fully collateralized	26,700,000
Liability recognized for the obligations	$ 897,000	$ 843,000

Represents the maximum potential amount of future payments which is fully collateralized.

No definition available.

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

- Definition

Represents the amount of recourse provisions that would enable the guarantor to recover from third parties any of the amounts paid under the guarantee (or each group of similar guarantees).

+ References

No definition available.

+ Details

Name:	nwbi_GuaranteeObligationsRecourseProvisionsAmount
Namespace Prefix:	nwbi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The fair value of financial liabilities, which are not recognized in the financial statements (off-balance sheet) because they fail to meet some other criterion for recognition.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 10

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=28364263&loc=d3e13433-108611

+ Details

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

- Details

Name:	us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 460

-SubTopic 10

-Section 50

-Paragraph 4

-Subparagraph (b)(1)

-URI http://asc.fasb.org/extlink&oid=6851643&loc=d3e12069-110248

+ Details

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

- Definition

Reflects the amount of cash required to fully fund agreements to provide advances to borrowers and lessees at stated interest rates.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 825

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6480020&loc=d3e61082-112788

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 825

-Section 50

-Paragraph 1

-Subparagraph (b)(2)

-URI http://asc.fasb.org/extlink&oid=6480020&loc=d3e61044-112788

+ Details

Name:	us-gaap_LoansAndLeasesReceivableCommitmentsFixedRates
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Reflects the amount of cash required to fully fund agreements to provide advances to borrowers and lessees at interest rates that increase or decrease depending on certain facts or circumstances.

+ References

+ Details

Name:	us-gaap_LoansAndLeasesReceivableCommitmentsVariableRates
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Carrying amount as of the balance sheet date of unearned revenue or income not otherwise specified in the taxonomy which is expected to be taken into income within one year or the normal operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.20)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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