Acquisitions - Summary of Supplemental Pro-forma Information (Detail) - Intervest Bancshares Corporation [Member] - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
Jun. 30, 2015	Jun. 30, 2014
Pro-forma Information [Line Items]
Net interest income - pro forma (unaudited)	$ 186,428	$ 143,484
Net income - pro forma (unaudited)	$ 88,745	$ 62,949
Diluted earnings per common share - pro forma (unaudited)	$ 1.01	$ 0.76

Acquisition Pro Forma Net Interest Income Net Income and Earnings Per Share [Line Items]

No definition available.

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- Definition

Business acquisitions pro forma net interest income as if the business combination or combinations had been completed at the beginning of a period.

+ References

No definition available.

+ Details

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- Definition

The pro forma diluted net income per share for a period as if the business combination or combinations had been completed at the beginning of a period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(2)-(3)

-URI http://asc.fasb.org/extlink&oid=56956515&loc=d3e1392-128463

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- Definition

The pro forma net Income or Loss for the period as if the business combination or combinations had been completed at the beginning of a period.

+ References

+ Details

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