Amortized cost, gross unrealized gains and losses, approximate fair value, weighted average yield and contractual maturities of investment securities held-to-maturity (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 122,072	$ 125,383
Gross Unrealized Gains	2,414	825
Gross Unrealized Losses	384	954
Fair Value	124,102	125,254
Weighted Average Yield	4.25%	4.28%
US Treasury Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	0	0
Weighted Average Yield	0.00%	0.00%
US Treasury Securities [Member] | One Year From Balance Sheet Date [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	0	0
Weighted Average Yield	0.00%	0.00%
US Treasury Securities [Member] | More Than One And Within Five Years From Balance Sheet Date [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	0	0
Weighted Average Yield	0.00%	0.00%
US Treasury Securities [Member] | More Than Five And Within Ten Years From Balance Sheet Date [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	0	0
Weighted Average Yield	0.00%	0.00%
US Treasury Securities [Member] | More Than Ten Years From Balance Sheet Date [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	0	0
Weighted Average Yield	0.00%	0.00%
Collateralized Mortgage Obligations Issued By Private Enterprise [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	0	160
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	9
Fair Value	0	151
Weighted Average Yield	0.00%	5.45%
Collateralized Mortgage Obligations Issued By Private Enterprise [Member] | One Year From Balance Sheet Date [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	0	0
Weighted Average Yield	0.00%	0.00%
Collateralized Mortgage Obligations Issued By Private Enterprise [Member] | More Than One And Within Five Years From Balance Sheet Date [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	0	0
Weighted Average Yield	0.00%	0.00%
Collateralized Mortgage Obligations Issued By Private Enterprise [Member] | More Than Five And Within Ten Years From Balance Sheet Date [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	0	0
Weighted Average Yield	0.00%	0.00%
Collateralized Mortgage Obligations Issued By Private Enterprise [Member] | More Than Ten Years From Balance Sheet Date [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	0	160
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	9
Fair Value	0	151
Weighted Average Yield	0.00%	5.45%
Collateralized Mortgage Obligations Issued By U S Government Sponsored Enterprises And U S Government [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	147
Gross Unrealized Gains	6
Gross Unrealized Losses	0
Fair Value	153
Weighted Average Yield	5.45%
Collateralized Mortgage Obligations Issued By U S Government Sponsored Enterprises And U S Government [Member] | More Than Ten Years From Balance Sheet Date [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	147
Gross Unrealized Gains	6
Gross Unrealized Losses	0
Fair Value	153
Weighted Average Yield	5.45%
Other Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	26,500	26,250
Gross Unrealized Gains	25	83
Gross Unrealized Losses	0	0
Fair Value	26,525	26,333
Weighted Average Yield	3.39%	3.41%
Other Securities [Member] | One Year From Balance Sheet Date [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	250	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	250	0
Weighted Average Yield	1.05%	0.00%
Other Securities [Member] | More Than One And Within Five Years From Balance Sheet Date [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	26,250	26,250
Gross Unrealized Gains	25	83
Gross Unrealized Losses	0	0
Fair Value	26,275	26,333
Weighted Average Yield	3.41%	3.41%
Other Securities [Member] | More Than Five And Within Ten Years From Balance Sheet Date [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	0	0
Weighted Average Yield	0.00%	0.00%
Other Securities [Member] | More Than Ten Years From Balance Sheet Date [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	0	0
Weighted Average Yield	0.00%	0.00%
US Government Sponsored Enterprises Debt Securities Member
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	0
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	0
Weighted Average Yield	0.00%
US Government Sponsored Enterprises Debt Securities Member | One Year From Balance Sheet Date [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	0
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	0
Weighted Average Yield	0.00%
US Government Sponsored Enterprises Debt Securities Member | More Than One And Within Five Years From Balance Sheet Date [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	0
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	0
Weighted Average Yield	0.00%
US Government Sponsored Enterprises Debt Securities Member | More Than Five And Within Ten Years From Balance Sheet Date [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	0
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	0
Weighted Average Yield	0.00%
US Government Sponsored Enterprises Debt Securities Member | More Than Ten Years From Balance Sheet Date [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	0
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	0
Weighted Average Yield	0.00%
Puerto Rico States And Political Subdivisions Debt Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	95,425	98,973
Gross Unrealized Gains	2,383	742
Gross Unrealized Losses	384	945
Fair Value	97,424	98,770
Weighted Average Yield	4.49%	4.51%
Puerto Rico States And Political Subdivisions Debt Securities [Member] | One Year From Balance Sheet Date [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	7,420	7,275
Gross Unrealized Gains	20	6
Gross Unrealized Losses	0	0
Fair Value	7,440	7,281
Weighted Average Yield	2.63%	2.24%
Puerto Rico States And Political Subdivisions Debt Securities [Member] | More Than One And Within Five Years From Balance Sheet Date [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	11,335	11,174
Gross Unrealized Gains	619	430
Gross Unrealized Losses	0	0
Fair Value	11,954	11,604
Weighted Average Yield	5.86%	5.80%
Puerto Rico States And Political Subdivisions Debt Securities [Member] | More Than Five And Within Ten Years From Balance Sheet Date [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	18,780	18,512
Gross Unrealized Gains	1,046	266
Gross Unrealized Losses	0	90
Fair Value	19,826	18,688
Weighted Average Yield	6.03%	5.99%
Puerto Rico States And Political Subdivisions Debt Securities [Member] | More Than Ten Years From Balance Sheet Date [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	57,890	62,012
Gross Unrealized Gains	698	40
Gross Unrealized Losses	384	855
Fair Value	$ 58,204	$ 61,197
Weighted Average Yield	3.96%	4.11%