Quarterly report pursuant to Section 13 or 15(d)

Investment Securities - Schedule of Amortized Cost and Estimated Fair Value of Investment Securities by Contractual Maturity (Detail)

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Investment Securities - Schedule of Amortized Cost and Estimated Fair Value of Investment Securities by Contractual Maturity (Detail) (USD $)
In Thousands, unless otherwise specified
Sep. 30, 2014
Dec. 31, 2013
Summary of Investment Holdings [Line Items]    
Available-for-Sale Within one year, Amortized Cost $ 15,702  
Available-for-Sale Over one year through five years, Amortized Cost 73,633  
Available-for-Sale Over five years through ten years, Amortized Cost 139,745  
Available-for-Sale Over ten years, Amortized Cost 100,305  
Available-for-Sale, Amortized Cost 1,139,173 549,113
Available-for-Sale Within one year, Estimated Fair Value 15,721  
Available-for-Sale Over one year through five years, Estimated Fair Value 73,247  
Available-for-Sale Over five years through ten years, Estimated Fair Value 136,900  
Available-for-Sale Over ten years, Estimated Fair Value 99,234  
Available-for-Sale, Estimated Fair Value 1,128,624 530,926
Collateralized mortgage obligations [Member]
   
Summary of Investment Holdings [Line Items]    
Available-for-Sale, Amortized Cost 197,784 130,636
Available-for-Sale, Estimated Fair Value 196,211 127,693
Mortgage-backed securities [Member]
   
Summary of Investment Holdings [Line Items]    
Available-for-Sale, Amortized Cost 588,638 222,768
Available-for-Sale, Estimated Fair Value 584,157 217,059
Other securities [Member]
   
Summary of Investment Holdings [Line Items]    
Available-for-Sale, Amortized Cost 22,916 3,030
Available-for-Sale, Estimated Fair Value 22,704 2,886
Equity security [Member]
   
Summary of Investment Holdings [Line Items]    
Available-for-Sale, Amortized Cost 450  
Available-for-Sale, Estimated Fair Value $ 450