Securities - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2013 Securities	Sep. 30, 2012	Sep. 30, 2013 Securities	Sep. 30, 2012	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Number of securities holdings	0		0
Shareholders' equity percentage	10.00%		10.00%
Amortized Cost	$ 708,303		$ 708,303		$ 712,637
Fair Value	700,531		700,531		737,311
Number of structured pooled trust preferred securities deemed to be other-than-temporarily impaired	4		4		4
Securities	340,446		340,446		264,813
Pooled Trust Preferred [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	800		800		800
Fair Value	776		776		600
Four Structured Pool Trust Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of Pooled Trust Securities	1		1
Amortized Cost	0		0		0
Other than temporary impairment recognized in earnings for available for sale securities	$ 0	$ 0	$ 0	$ 0

Number of pooled trust securities.

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- Definition

Number of securities holdings.

+ References

No definition available.

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- Definition

Other than temporarily impaired structured pooled trust preferred securities number.

+ References

No definition available.

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- Definition

Shareholders equity percentage.

+ References

No definition available.

+ Details

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- 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 Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 5

-Subparagraph (aa)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

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

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- 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

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.2)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

The amount of other than temporary impairment losses on investments in debt and equity securities categorized as Available-for-sale which have been recognized in earnings during the period. Such impairment losses consist of other than temporary impairments (OTTI) on equity securities, credit losses on investments in debt securities, and when the entity intends to sell an impaired debt security or it is more likely than not that the entity will be required to sell the impaired debt security before recovery of its amortized cost basis.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563

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- Definition

The fair value of trading securities that serve as collateral for borrowings.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=28368275&loc=d3e5086-111524

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