Amortized Cost, Unrealized Gross Gains and Losses Recognized in Accumulated Other Comprehensive Income (Loss), and Fair Value of Securities Available-for-Sale (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 571,058	$ 500,128
Gross Unrealized Gains	16,739	16,808
Gross Unrealized Losses	(195)	(92)
Fair Value	587,602	516,844
U.S. Treasury and Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	23,570	6,340
Gross Unrealized Gains	40	82
Gross Unrealized Losses	(138)	0
Fair Value	23,472	6,422
Corporate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	0	1,003
Gross Unrealized Gains	0	2
Gross Unrealized Losses	0	0
Fair Value	0	1,005
Obligations of State and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	71,352	60,606
Gross Unrealized Gains	5,145	4,195
Gross Unrealized Losses	(12)	(2)
Fair Value	76,485	64,799
Mortgage-backed Securities - Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	475,452	431,495
Gross Unrealized Gains	11,505	12,529
Gross Unrealized Losses	(45)	(90)
Fair Value	486,912	443,934
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	684	684
Gross Unrealized Gains	49	0
Gross Unrealized Losses	0	0
Fair Value	$ 733	$ 684

Amortized Cost, Unrealized Gross Gains and Losses Recognized in Accumulated Other Comprehensive Income (Loss), and Fair Value of Securities Available-for-Sale (Detail) (USD $)
In Thousands, unless otherwise specified

Dec. 31, 2012

Dec. 31, 2011

Schedule of Available-for-sale Securities [Line Items]

Amortized Cost

$ 571,058

$ 500,128

Gross Unrealized Gains

16,739

16,808

Gross Unrealized Losses

(195)

(92)

Fair Value

587,602

516,844

U.S. Treasury and Agency Securities [Member]

Schedule of Available-for-sale Securities [Line Items]

Amortized Cost

23,570

6,340

Gross Unrealized Gains

Gross Unrealized Losses

(138)

Fair Value

23,472

6,422

Corporate Securities [Member]

Schedule of Available-for-sale Securities [Line Items]

Amortized Cost

1,003

Gross Unrealized Gains

Gross Unrealized Losses

Fair Value

1,005

Obligations of State and Political Subdivisions [Member]

Schedule of Available-for-sale Securities [Line Items]

Amortized Cost

71,352

60,606

Gross Unrealized Gains

5,145

4,195

Gross Unrealized Losses

(12)

(2)

Fair Value

76,485

64,799

Mortgage-backed Securities - Residential [Member]

Schedule of Available-for-sale Securities [Line Items]

Amortized Cost

475,452

431,495

Gross Unrealized Gains

11,505

12,529

Gross Unrealized Losses

(45)

(90)

Fair Value

486,912

443,934

Equity Securities [Member]

Schedule of Available-for-sale Securities [Line Items]

Amortized Cost

684

Gross Unrealized Gains

Gross Unrealized Losses

Fair Value

$ 733

$ 684

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 15D

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 12

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 16

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 15C

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=7534914&loc=d3e22054-111558

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 15E

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 13

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 9: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 14

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 10: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 22

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

- Definition

This item represents the cost of debt and equity 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.

+ References+ Details

- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

+ References+ Details