2.2.0.7 true Consolidated Statements of Changes in Stockholders' Equity (Unaudited) (Parenthetical) (USD $) 0141 - Statement - Consolidated Statements of Changes in Stockholders' Equity (Unaudited) (Parenthetical) true false false false 1 USD false false USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 USDEPS Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares xbrli 0 $ false 2 USD false false USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 USDEPS Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares xbrli 0 $ 2 Common stock issued for the acquisition of Harleysville National Corporation 2 us-gaap_StockIssuedDuringPeriodSharesAcquisitions us-gaap true na duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 20295305 20295305 false false false 2 false false false false 0 0 false false false xbrli:sharesItemType shares Number of shares of stock issued during the period pursuant to acquisitions. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 141 -Paragraph 53 -Subparagraph b Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 141 -Paragraph 51 -Subparagraph d Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30 -Article 5 false 3 Proceeds from follow-on stock offering, net of related expenses, shares 2 us-gaap_StockIssuedDuringPeriodSharesNewIssues us-gaap true na duration No definition available. false false false false false false false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false true false false 31050000 31050000 false false false xbrli:sharesItemType shares Number of new stock issued during the period. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 12 -Paragraph 10 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30 -Article 5 false 4 ESOP shares committed to be released 2 us-gaap_StockIssuedDuringPeriodSharesEmployeeStockOwnershipPlan us-gaap true na duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 131435 131435 false false false 2 false true false false 115366 115366 false false false xbrli:sharesItemType shares Number of stock issued during the period as a result of employee stock ownership plan (ESOP). Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 12 -Paragraph 10 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30 -Article 5 false 5 Common stock, dividend per share 2 us-gaap_CommonStockDividendsPerShareDeclared us-gaap true na duration No definition available. false false false false false false false false false false false terselabel true 1 true true false false 0.28 0.28 false false false 2 true true false false 0.28 0.28 false false false us-types:perShareItemType decimal Aggregate dividends declared during the period for each share of common stock outstanding. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 false 6 Exercise of stock options and restricted stock activity, shares 2 fnfg_ExerciseOfStockOptionsAndRestrictedStockActivityShares fnfg false na duration Number of shares of stock issued for exercise of stock options and net change in number of shares of stock related to... false false false false false false false false false false false verboselabel false 1 false true false false 529869 529869 false false false 2 false true false false 151346 151346 false false false xbrli:sharesItemType shares Number of shares of stock issued for exercise of stock options and net change in number of shares of stock related to issuance of restricted stock awards, forfeitures of restricted stock awards, and repurchases of shares of stock related to taxes on vestings of restricted stock awards. No authoritative reference available. false 7 Common stock 0 na true na na No definition available. false true false false false false false false false false false http://fnfg.com/role/statementsofchangesinstockholdersequityparenthetical false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false false 5 USD true false false false us-gaap_CommonStockMember us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_CommonStockMember us-gaap_StatementEquityComponentsAxis explicitMember Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 $ false 6 USD true false false false us-gaap_CommonStockMember us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_CommonStockMember us-gaap_StatementEquityComponentsAxis explicitMember Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 $ na No definition available. No authoritative reference available. false 8 Common stock issued for the acquisition of Harleysville National Corporation 2 us-gaap_StockIssuedDuringPeriodSharesAcquisitions us-gaap true na duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 20295305 20295305 false false false 2 false false false false 0 0 false false false xbrli:sharesItemType shares Number of shares of stock issued during the period pursuant to acquisitions. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 141 -Paragraph 53 -Subparagraph b Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 141 -Paragraph 51 -Subparagraph d Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30 -Article 5 false 9 Proceeds from follow-on stock offering, net of related expenses, shares 2 us-gaap_StockIssuedDuringPeriodSharesNewIssues us-gaap true na duration No definition available. false false false false false false false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false true false false 31050000 31050000 false false false xbrli:sharesItemType shares Number of new stock issued during the period. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 12 -Paragraph 10 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30 -Article 5 false 13 Additional paid-in capital 0 na true na na No definition available. false true false false false false false false false false false http://fnfg.com/role/statementsofchangesinstockholdersequityparenthetical false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false false 7 USD true false false false us-gaap_AdditionalPaidInCapitalMember us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_AdditionalPaidInCapitalMember us-gaap_StatementEquityComponentsAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 $ false 8 USD true false false false us-gaap_AdditionalPaidInCapitalMember us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_AdditionalPaidInCapitalMember us-gaap_StatementEquityComponentsAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 $ na No definition available. No authoritative reference available. false 14 Common stock issued for the acquisition of Harleysville National Corporation 2 us-gaap_StockIssuedDuringPeriodSharesAcquisitions us-gaap true na duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 20295305 20295305 false false false 2 false false false false 0 0 false false false xbrli:sharesItemType shares Number of shares of stock issued during the period pursuant to acquisitions. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 141 -Paragraph 53 -Subparagraph b Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 141 -Paragraph 51 -Subparagraph d Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30 -Article 5 false 15 Proceeds from follow-on stock offering, net of related expenses, shares 2 us-gaap_StockIssuedDuringPeriodSharesNewIssues us-gaap true na duration No definition available. false false false false false false false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false true false false 31050000 31050000 false false false xbrli:sharesItemType shares Number of new stock issued during the period. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 12 -Paragraph 10 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30 -Article 5 false 16 ESOP shares committed to be released 2 us-gaap_StockIssuedDuringPeriodSharesEmployeeStockOwnershipPlan us-gaap true na duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 131435 131435 false false false 2 false true false false 115366 115366 false false false xbrli:sharesItemType shares Number of stock issued during the period as a result of employee stock ownership plan (ESOP). Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 12 -Paragraph 10 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30 -Article 5 false 18 Exercise of stock options and restricted stock activity, shares 2 fnfg_ExerciseOfStockOptionsAndRestrictedStockActivityShares fnfg false na duration Number of shares of stock issued for exercise of stock options and net change in number of shares of stock related to... false false false false false false false false false false false verboselabel false 1 false true false false 529869 529869 false false false 2 false true false false 151346 151346 false false false xbrli:sharesItemType shares Number of shares of stock issued for exercise of stock options and net change in number of shares of stock related to issuance of restricted stock awards, forfeitures of restricted stock awards, and repurchases of shares of stock related to taxes on vestings of restricted stock awards. No authoritative reference available. false 19 Retained earnings 0 na true na na No definition available. false true false false false false false false false false false http://fnfg.com/role/statementsofchangesinstockholdersequityparenthetical false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false false 9 USD true false false false us-gaap_RetainedEarningsMember us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_RetainedEarningsMember us-gaap_StatementEquityComponentsAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 USDEPS Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares xbrli 0 $ false 10 USD true false false false us-gaap_RetainedEarningsMember us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_RetainedEarningsMember us-gaap_StatementEquityComponentsAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 USDEPS Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares xbrli 0 $ na No definition available. No authoritative reference available. false 23 Common stock, dividend per share 2 us-gaap_CommonStockDividendsPerShareDeclared us-gaap true na duration No definition available. false false false false false false false false false false false terselabel true 1 true true false false 0.28 0.28 false false false 2 true true false false 0.28 0.28 false false false us-types:perShareItemType decimal Aggregate dividends declared during the period for each share of common stock outstanding. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 false 24 Exercise of stock options and restricted stock activity, shares 2 fnfg_ExerciseOfStockOptionsAndRestrictedStockActivityShares fnfg false na duration Number of shares of stock issued for exercise of stock options and net change in number of shares of stock related to... false false false false false false false false false false false verboselabel false 1 false true false false 529869 529869 false false false 2 false true false false 151346 151346 false false false xbrli:sharesItemType shares Number of shares of stock issued for exercise of stock options and net change in number of shares of stock related to issuance of restricted stock awards, forfeitures of restricted stock awards, and repurchases of shares of stock related to taxes on vestings of restricted stock awards. No authoritative reference available. false 25 Common stock held by ESOP 0 na true na na No definition available. false true false false false false false false false false false http://fnfg.com/role/statementsofchangesinstockholdersequityparenthetical false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false false 11 USD true false false false fnfg_CommonStockHeldByEsopMember us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi fnfg_CommonStockHeldByEsopMember us-gaap_StatementEquityComponentsAxis explicitMember Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 $ false 12 USD true false false false fnfg_CommonStockHeldByEsopMember us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi fnfg_CommonStockHeldByEsopMember us-gaap_StatementEquityComponentsAxis explicitMember Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 $ na No definition available. No authoritative reference available. false 28 ESOP shares committed to be released 2 us-gaap_StockIssuedDuringPeriodSharesEmployeeStockOwnershipPlan us-gaap true na duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 131435 131435 false false false 2 false true false false 115366 115366 false false false xbrli:sharesItemType shares Number of stock issued during the period as a result of employee stock ownership plan (ESOP). Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 12 -Paragraph 10 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30 -Article 5 false 31 Treasury stock 0 na true na na No definition available. false true false false false false false false false false false http://fnfg.com/role/statementsofchangesinstockholdersequityparenthetical false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false false 13 USD true false false false us-gaap_TreasuryStockMember us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_TreasuryStockMember us-gaap_StatementEquityComponentsAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 $ false 14 USD true false false false us-gaap_TreasuryStockMember us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_TreasuryStockMember us-gaap_StatementEquityComponentsAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 $ na No definition available. No authoritative reference available. false 36 Exercise of stock options and restricted stock activity, shares 2 fnfg_ExerciseOfStockOptionsAndRestrictedStockActivityShares fnfg false na duration Number of shares of stock issued for exercise of stock options and net change in number of shares of stock related to... false false false false false false false false false false false verboselabel false 1 false true false false 529869 529869 false false false 2 false true false false 151346 151346 false false false xbrli:sharesItemType shares Number of shares of stock issued for exercise of stock options and net change in number of shares of stock related to issuance of restricted stock awards, forfeitures of restricted stock awards, and repurchases of shares of stock related to taxes on vestings of restricted stock awards. No authoritative reference available. false 2 20 false UnKnown NoRounding NoRounding false true