INVESTMENT SECURITIES - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended
Mar. 31, 2015 numberofcontracts	Mar. 31, 2014	Dec. 31, 2014
Schedule Of Investments [Line Items]
Percentage Of Debt Securities Government And Government Sponsored Agencies	96.00%
Amortized cost of private label of mortgage backed security	$ 43,000,000
Credit related impairment loss is related to Private label MBS	156,000
Minimum Credit Score	700fbp_MinimumCreditScore
Maximum loan to value ratio	80.00%fbp_MaximumLoanToValueRatio
Proceeds From Maturities Prepayments And Calls Of Available For Sale Securities	53,596,000	45,422,000
Total investment securities available for sale	1,974,226,000us-gaap_AvailableForSaleSecurities		1,965,666,000us-gaap_AvailableForSaleSecurities
Fair value	1,974,226,000us-gaap_AvailableForSaleSecurities		1,965,666,000us-gaap_AvailableForSaleSecurities
Amortized cost	1,977,681,000		1,976,261,000
Unrealized losses	29,867,000		30,405,000
Weighted average yield	2.48%fbp_SecuritiesWeightedAverageYield		2.49%fbp_SecuritiesWeightedAverageYield
Puerto Rico Government obligations [Member]
Schedule Of Investments [Line Items]
Total investment securities available for sale	41,500,000		27,408,000
Fair value	41,500,000		27,408,000
Amortized cost	65,500,000
Change in net unrealized gains	$ (6,100,000)

Maximum loan to value ratio.

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Minimum original credit score (FICO) related to underlying mortgage loans.

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- Definition

Other than temporary impairment losses, investments related to mortgage back security.

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Percentage of total US government and sponsored agencies securities in relation to total investment securities.

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No definition available.

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Percentage of weighted average yield securities.

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No definition available.

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- Definition

This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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This item represents the pretax change in net unrealized holding gain (loss) on available-for-sale securities that has been included in accumulated other comprehensive income, a separate component of shareholders' equity, during the period.

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Amount of unrealized loss before deducting unrealized gain on investments in available-for-sale securities.

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The cash inflow associated with maturities (principal being due), prepayments and calls (requests of early payments) on securities not classified as either held-to-maturity securities or trading securities which are classified as available-for-sale securities.

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