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Loans receivable (Details 11) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Credit quality indicators    
Total loans $ 6,064,864us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome $ 5,989,891us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
Pass    
Credit quality indicators    
Total loans 5,797,031us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 5,712,244us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Special mention    
Credit quality indicators    
Total loans 66,525us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 60,598us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Substandard    
Credit quality indicators    
Total loans 190,685us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 212,948us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Doubtful    
Credit quality indicators    
Total loans 9,199us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_DoubtfulMember		 2,677us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_DoubtfulMember
Loss    
Credit quality indicators    
Total loans 1,424us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_UnlikelyToBeCollectedFinancingReceivableMember		 1,424us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_UnlikelyToBeCollectedFinancingReceivableMember
Special mention or substandard | Minimum    
Credit quality indicators    
Total loans 1,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_InternalCreditAssessmentAxis
= nwbi_SpecialMentionAndSubstandardMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		  
Personal Banking    
Credit quality indicators    
Total loans 3,839,565us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_PersonalBankingMember		 3,830,331us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_PersonalBankingMember
Personal Banking | Pass    
Credit quality indicators    
Total loans 3,820,068us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_PersonalBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 3,807,741us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_PersonalBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Personal Banking | Substandard    
Credit quality indicators    
Total loans 18,073us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_PersonalBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 21,166us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_PersonalBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Personal Banking | Loss    
Credit quality indicators    
Total loans 1,424us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_PersonalBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_UnlikelyToBeCollectedFinancingReceivableMember		 1,424us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_PersonalBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_UnlikelyToBeCollectedFinancingReceivableMember
Personal Banking | Residential mortgage loans    
Credit quality indicators    
Total loans 2,543,870us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ResidentialMortgageMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_PersonalBankingMember		 2,521,456us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ResidentialMortgageMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_PersonalBankingMember
Personal Banking | Residential mortgage loans | Pass    
Credit quality indicators    
Total loans 2,531,595us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ResidentialMortgageMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_PersonalBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 2,507,269us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ResidentialMortgageMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_PersonalBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Personal Banking | Residential mortgage loans | Substandard    
Credit quality indicators    
Total loans 10,851us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ResidentialMortgageMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_PersonalBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 12,763us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ResidentialMortgageMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_PersonalBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Personal Banking | Residential mortgage loans | Loss    
Credit quality indicators    
Total loans 1,424us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ResidentialMortgageMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_PersonalBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_UnlikelyToBeCollectedFinancingReceivableMember		 1,424us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ResidentialMortgageMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_PersonalBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_UnlikelyToBeCollectedFinancingReceivableMember
Personal Banking | Home equity loans    
Credit quality indicators    
Total loans 1,055,739us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_PersonalBankingMember		 1,066,131us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_PersonalBankingMember
Personal Banking | Home equity loans | Pass    
Credit quality indicators    
Total loans 1,050,092us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_PersonalBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 1,059,525us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_PersonalBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Personal Banking | Home equity loans | Substandard    
Credit quality indicators    
Total loans 5,647us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_PersonalBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 6,606us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_PersonalBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Personal Banking | Other consumer loans    
Credit quality indicators    
Total loans 239,956us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_PersonalBankingMember		 242,744us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_PersonalBankingMember
Personal Banking | Other consumer loans | Pass    
Credit quality indicators    
Total loans 238,381us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_PersonalBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 240,947us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_PersonalBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Personal Banking | Other consumer loans | Substandard    
Credit quality indicators    
Total loans 1,575us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_PersonalBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 1,797us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_PersonalBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Business Banking    
Credit quality indicators    
Total loans 2,225,299us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_BusinessBankingMember		 2,159,560us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_BusinessBankingMember
Business Banking | Pass    
Credit quality indicators    
Total loans 1,976,963us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_BusinessBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 1,904,503us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_BusinessBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Business Banking | Special mention    
Credit quality indicators    
Total loans 66,525us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_BusinessBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 60,598us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_BusinessBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Business Banking | Substandard    
Credit quality indicators    
Total loans 172,612us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_BusinessBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 191,782us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_BusinessBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Business Banking | Doubtful    
Credit quality indicators    
Total loans 9,199us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_BusinessBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_DoubtfulMember		 2,677us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_BusinessBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_DoubtfulMember
Business Banking | Commercial real estate loans    
Credit quality indicators    
Total loans 1,856,574us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_BusinessBankingMember		 1,801,184us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_BusinessBankingMember
Business Banking | Commercial real estate loans | Pass    
Credit quality indicators    
Total loans 1,671,331us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_BusinessBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 1,618,269us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_BusinessBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Business Banking | Commercial real estate loans | Special mention    
Credit quality indicators    
Total loans 43,874us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_BusinessBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 36,908us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_BusinessBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Business Banking | Commercial real estate loans | Substandard    
Credit quality indicators    
Total loans 141,369us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_BusinessBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 145,502us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_BusinessBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Business Banking | Commercial real estate loans | Doubtful    
Credit quality indicators    
Total loans   505us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_BusinessBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_DoubtfulMember
Business Banking | Commercial loans    
Credit quality indicators    
Total loans 368,725us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_BusinessBankingMember		 358,376us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_BusinessBankingMember
Business Banking | Commercial loans | Pass    
Credit quality indicators    
Total loans 305,632us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_BusinessBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 286,234us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_BusinessBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Business Banking | Commercial loans | Special mention    
Credit quality indicators    
Total loans 22,651us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_BusinessBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 23,690us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_BusinessBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Business Banking | Commercial loans | Substandard    
Credit quality indicators    
Total loans 31,243us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_BusinessBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 46,280us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_BusinessBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Business Banking | Commercial loans | Doubtful    
Credit quality indicators    
Total loans $ 9,199us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_BusinessBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_DoubtfulMember		 $ 2,172us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nwbi_BusinessBankingMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_DoubtfulMember