Fair Value Measurements (Additional Information about Assets Measured At Fair Value on a Recurring Basis) (Details) (USD $) In Thousands	6 Months Ended	12 Months Ended
Jun. 30, 2011	Dec. 31, 2010
Balance at beginning of period	$ 17,594	$ 15,587
Total gains (losses) - realized/unrealized, Included in earnings	(48)	(2,281)
Total gains (losses) - realized/unrealized, Included in other comprehensive income	1,567	4,288
Redemptions	(6,095)
Balance at end of period	13,018	17,594
Collateralized Debt Obligations [Member]
Balance at beginning of period	5,974	4,824
Total gains (losses) - realized/unrealized, Included in earnings		(2,281)
Total gains (losses) - realized/unrealized, Included in other comprehensive income	631	3,431
Balance at end of period	6,605	5,974
Other Debt Securities [Member]
Balance at beginning of period	11,245	10,430
Total gains (losses) - realized/unrealized, Included in earnings	(48)
Total gains (losses) - realized/unrealized, Included in other comprehensive income	844	815
Redemptions	(6,095)
Balance at end of period	5,946	11,245
Equity Securities [Member]
Balance at beginning of period	375	333
Total gains (losses) - realized/unrealized, Included in other comprehensive income	92	42
Balance at end of period	$ 467	$ 375

Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Redemptions

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Namespace Prefix:	fnb
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

This element represents total gains or losses for the period (realized and unrealized), arising from assets measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in earnings or resulted in a change in net asset value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 157
-Paragraph 32
-Subparagraph c(1)

+ Details

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Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

This element represents total gains or losses for the period (realized and unrealized), arising from assets measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in other comprehensive income (a separate component of shareholders' equity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 157
-Paragraph 32
-Subparagraph c(1)

+ Details

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Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
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Period Type:	duration

- Definition

This element represents an asset measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 157
-Paragraph 32
-Subparagraph c

+ Details

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