Annual report pursuant to Section 13 and 15(d)

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

v2.4.1.9
Investment Securities - Schedule of Amortized Cost and Estimated Fair Value of Investment Securities by Contractual Maturity (Detail) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Summary of Investment Holdings [Line Items]    
Available-for-Sale Within one year, Amortized Cost $ 17,693us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost  
Available-for-Sale Over one year through five years, Amortized Cost 45,470us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost  
Available-for-Sale Over five years through ten years, Amortized Cost 127,601us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost  
Available-for-Sale Over ten years, Amortized Cost 87,191us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost  
Available-for-Sale, Amortized Cost 1,061,703us-gaap_AvailableForSaleSecuritiesAmortizedCost 549,113us-gaap_AvailableForSaleSecuritiesAmortizedCost
Available-for-Sale Within one year, Estimated Fair Value 17,636us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue  
Available-for-Sale Over one year through five years, Estimated Fair Value 45,450us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue  
Available-for-Sale Over five years through ten years, Estimated Fair Value 126,506us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue  
Available-for-Sale Over ten years, Estimated Fair Value 86,485us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue  
Available-for-Sale, Estimated Fair Value 1,060,717us-gaap_AvailableForSaleSecurities 530,926us-gaap_AvailableForSaleSecurities
Collateralized mortgage obligations [Member]    
Summary of Investment Holdings [Line Items]    
Available-for-Sale, Amortized Cost 188,704us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_CollateralizedMortgageObligationsMember 		130,636us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_CollateralizedMortgageObligationsMember
Available-for-Sale, Estimated Fair Value 188,047us-gaap_AvailableForSaleSecurities
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_CollateralizedMortgageObligationsMember 		127,693us-gaap_AvailableForSaleSecurities
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_CollateralizedMortgageObligationsMember
Mortgage-backed securities [Member]    
Summary of Investment Holdings [Line Items]    
Available-for-Sale, Amortized Cost 571,678us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember 		222,768us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Available-for-Sale, Estimated Fair Value 573,286us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember 		217,059us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Other securities [Member]    
Summary of Investment Holdings [Line Items]    
Available-for-Sale, Amortized Cost 22,916us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember 		3,030us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember
Available-for-Sale, Estimated Fair Value 22,893us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember 		2,886us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember
Equity securities [Member]    
Summary of Investment Holdings [Line Items]    
Available-for-Sale, Amortized Cost 450us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember 		 
Available-for-Sale, Estimated Fair Value $ 414us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember