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

The non-accruing portion of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings.

No definition available.

Name:	nwbi_FinancingReceivableModificationsRecordedInvestmentNonAccrual
Namespace Prefix:	nwbi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

The allowance for loan and lease losses represents the reserve to cover probable credit losses related to all loans and leases, as well as probable credit losses inherent in the remainder of the loan portfolio as of the balance sheet date excluding unallocated amounts.

No definition available.

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

Amount of allowance for credit losses related to receivables which had been measured under a general allowance for credit losses methodology that are now identified as troubled debt restructurings.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 40

-Section 65

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=7484272&loc=SL7484277-172609

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

- Details

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

The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 40

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=25495931&loc=d3e18845-111554

Name:	us-gaap_FinancingReceivableModificationsRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Recorded investment in financing receivables that are 90 days or more past due and still accruing.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 7

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=28368275&loc=d3e5111-111524

Name:	us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date.

Name:	us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=28368275&loc=d3e5074-111524

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4428-111522