Goodwill and Other Intangible Assets - Schedule of Definite-Lived Intangible Assets (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 78,968	$ 57,665
Accumulated Amortization	(38,851)	(37,304)
Net Carrying Amount	40,117us-gaap_FiniteLivedIntangibleAssetsNet	20,361us-gaap_FiniteLivedIntangibleAssetsNet
Core Deposit Intangibles [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	77,252	55,949
Accumulated Amortization	(37,818)	(36,354)
Net Carrying Amount	39,434	19,595
Customer Relationship Intangible Asset [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,348	1,348
Accumulated Amortization	(865)	(822)
Net Carrying Amount	483	526
Noncompete Agreements [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	163	163
Accumulated Amortization	(105)	(82)
Net Carrying Amount	58	81
Other Intangible Assets [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	205	205
Accumulated Amortization	(63)	(46)
Net Carrying Amount	$ 142	$ 159

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Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275

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- Definition

Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

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Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

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