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

Name:	nwbi_FinancingReceivableModificationsAbstract
Namespace Prefix:	nwbi_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

The amount of financing receivables that have been modified by troubled debt restructurings and were paid off during the reporting period.

No definition available.

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

Represents the number of financing receivables that have been modified by troubled debt restructurings as of balance sheet date.

No definition available.

Name:	nwbi_FinancingReceivableModificationsNumberOfContract
Namespace Prefix:	nwbi_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Name:	nwbi_FinancingReceivableModificationsNumberOfContractRollForward
Namespace Prefix:	nwbi_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

The number of financing receivables that have been modified by troubled debt restructurings and were charged off during the reporting period.

No definition available.

Name:	nwbi_FinancingReceivableModificationsNumberOfContractsChargedOff
Namespace Prefix:	nwbi_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

The number of financing receivables that have been modified by troubled debt restructurings and were paid off during the reporting period.

No definition available.

Name:	nwbi_FinancingReceivableModificationsNumberOfContractsPaidOff
Namespace Prefix:	nwbi_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

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

No definition available.

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

The amount of additions during the period in recorded investment related to financing receivables that has been modified by troubled debt restructurings.

No definition available.

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

The amount of net paydowns out of recorded investment related to financing receivables that have been modified by troubled debt restructurings.

No definition available.

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

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

Name:	nwbi_FinancingReceivableModificationsRecordedInvestmentRollForward
Namespace Prefix:	nwbi_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Name:	nwbi_FinancingReceivableModificationsThatSubsequentlyDefaultedAbstract
Namespace Prefix:	nwbi_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Pre-modification amount of outstanding recorded investment related to financing receivables (as of the balance sheet date) that have been modified by troubled debt restructurings and then subsequently defaulted during the reporting period.

No definition available.

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

The increase decrease in the 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.

No definition available.

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

Represents the period of time to return TDRs included in non-performing loans to performing status through the fulfilling of contractual terms.

No definition available.

Name:	nwbi_PeriodToReturnTroubledDebtRestructuredLoansIncludedInNonPerformingLoansToPerformingStatus
Namespace Prefix:	nwbi_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

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

Number of 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 10

-Section 50

-Paragraph 33

-URI http://asc.fasb.org/extlink&oid=28368275&loc=SL6953676-111524

Name:	us-gaap_FinancingReceivableModificationsNumberOfContracts2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Post-modification amount of investment in financing receivables modified by troubled debt restructurings.

Name:	us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Pre-modification amount of investment in financing receivables modified by troubled debt restructurings.

Name:	us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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

Number of financing receivables that have been modified by troubled debt restructurings within the previous 12 months and for which there was a payment default.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 34

-URI http://asc.fasb.org/extlink&oid=28368275&loc=SL6953682-111524

Name:	us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Amount of investment related to financing receivables modified by troubled debt restructurings within the previous 12 months, for which there was a payment default.

Name:	us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Reflects the amount of the write-down related to a troubled debt restructuring.