Mergers And Acquisitions (Details) (USD $) In Thousands, except Share data	Dec. 31, 2010	Dec. 31, 2010 Comm Bancorp Inc [Member]	Jun. 15, 2011 Parkvale Financial Corporation [Member]
Assets acquired as a result of merger		$ 625,570	$ 1,800,000
Loans acquired as a result of merger		445,271
Deposits acquired as a result of merger		561,796
Value of acquisition		75,547	130,000
Shares entitled to the shareholders			2.178
Cash paid for acquisition of CBI		17,202
Common stock issued for exchange in merger	5,940,742	1,719,820
Goodwill recorded as a result of merger		38,658
Core deposit intangible recorded as a result of merger		$ 4,785

Business Acquisition Purchase Price Allocation Core Deposit Intangible Acquired

Name:	fnb_BusinessAcquisitionPurchasePriceAllocationCoreDepositIntangibleAcquired
Namespace Prefix:	fnb
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Business Acquisition Purchase Price Allocation Deposits Acquired

+ Details

Name:	fnb_BusinessAcquisitionPurchasePriceAllocationDepositsAcquired
Namespace Prefix:	fnb
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Business Acquisition Purchase Price Allocation Loans Receivable Acquired

+ Details

Name:	fnb_BusinessAcquisitionPurchasePriceAllocationLoansReceivableAcquired
Namespace Prefix:	fnb
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Business Acquisition Shares Entitled to Acquiree's Shareholders

+ Details

Name:	fnb_BusinessAcquisitionSharesEntitledToAcquireesShareholders
Namespace Prefix:	fnb
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Common stock issued for merger

+ Details

Name:	fnb_CommonStockIssuedForMerger
Namespace Prefix:	fnb
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of cash paid to acquire the entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 141R
-Paragraph 68
-Subparagraph f(1)

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 141
-Paragraph 51
-Subparagraph d

+ Details

Name:	us-gaap_BusinessAcquisitionCostOfAcquiredEntityCashPaid
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount of acquisition cost of a business combination allocated to assets acquired.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 141
-Paragraph 37
-Subparagraph g

+ Details

Name:	us-gaap_BusinessAcquisitionPurchasePriceAllocationAssetsAcquired
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The total purchase price of the acquired entity. This includes cash paid to equity interest holders of the acquired entity, fair value of debt and equity securities issued to equity holders of the acquired entity, and transaction costs paid to third parties to consummate the acquisition.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 141
-Paragraph 51
-Subparagraph d

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 141
-Paragraph 35

+ Details

Name:	us-gaap_BusinessAcquisitionPurchasePriceAllocationAssetsAcquiredLiabilitiesAssumedNet
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of goodwill arising from a business combination, which is the excess of the cost of the acquired entity over the amounts assigned to assets acquired and liabilities assumed.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 141
-Paragraph 52
-Subparagraph c

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 141
-Paragraph 53
-Subparagraph d

+ Details

Name:	us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillAmount
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant