XML 29 R79.htm IDEA: XBRL DOCUMENT v2.4.1.9
Loans, Leases and Allowance for Credit Losses - Troubled Debt Restructured Loans by Class for Which There was Payment Default (Detail) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
SecurityLoan
Dec. 31, 2013
SecurityLoan
Dec. 31, 2012
SecurityLoan
Financing Receivable, Modifications [Line Items]      
Number of Loans 8us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1 15us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1 35us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
Recorded Investment $ 1,950us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1 $ 6,370us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1 $ 34,387us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
Residential real estate [Member]      
Financing Receivable, Modifications [Line Items]      
Number of Loans 1us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_ResidentialRealEstateMember		 4us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_ResidentialRealEstateMember		 7us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_ResidentialRealEstateMember
Recorded Investment 202us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_ResidentialRealEstateMember		 955us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_ResidentialRealEstateMember		 8,014us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_ResidentialRealEstateMember
Consumer [Member]      
Financing Receivable, Modifications [Line Items]      
Number of Loans 0us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_ConsumerLoanMember		 0us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_ConsumerLoanMember		 2us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_ConsumerLoanMember
Recorded Investment 0us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_ConsumerLoanMember		 0us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_ConsumerLoanMember		 414us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_ConsumerLoanMember
Owner occupied [Member] | Commercial real estate [Member]      
Financing Receivable, Modifications [Line Items]      
Number of Loans 2us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_CommercialRealEstateOwnerOccupiedMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialRealEstateMember		 3us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_CommercialRealEstateOwnerOccupiedMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialRealEstateMember		 10us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_CommercialRealEstateOwnerOccupiedMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialRealEstateMember
Recorded Investment 395us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_CommercialRealEstateOwnerOccupiedMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialRealEstateMember		 2,506us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_CommercialRealEstateOwnerOccupiedMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialRealEstateMember		 10,611us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_CommercialRealEstateOwnerOccupiedMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialRealEstateMember
Non-owner occupied [Member] | Commercial real estate [Member]      
Financing Receivable, Modifications [Line Items]      
Number of Loans 2us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_CommercialRealEstateNonOwnerOccupiedMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialRealEstateMember		 3us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_CommercialRealEstateNonOwnerOccupiedMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialRealEstateMember		 3us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_CommercialRealEstateNonOwnerOccupiedMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialRealEstateMember
Recorded Investment 984us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_CommercialRealEstateNonOwnerOccupiedMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialRealEstateMember		 1,490us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_CommercialRealEstateNonOwnerOccupiedMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialRealEstateMember		 4,442us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_CommercialRealEstateNonOwnerOccupiedMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialRealEstateMember
Multi-family [Member] | Commercial real estate [Member]      
Financing Receivable, Modifications [Line Items]      
Number of Loans 0us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_CommercialRealEstateMultiFamilyMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialRealEstateMember		 0us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_CommercialRealEstateMultiFamilyMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialRealEstateMember		 1us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_CommercialRealEstateMultiFamilyMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialRealEstateMember
Recorded Investment 0us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_CommercialRealEstateMultiFamilyMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialRealEstateMember		 0us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_CommercialRealEstateMultiFamilyMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialRealEstateMember		 193us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_CommercialRealEstateMultiFamilyMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialRealEstateMember
Commercial [Member] | Commercial and industrial [Member]      
Financing Receivable, Modifications [Line Items]      
Number of Loans 3us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_CommercialAndIndustrialCommercialMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= wal_CommercialAndIndustrialMember		 3us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_CommercialAndIndustrialCommercialMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= wal_CommercialAndIndustrialMember		 7us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_CommercialAndIndustrialCommercialMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= wal_CommercialAndIndustrialMember
Recorded Investment 369us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_CommercialAndIndustrialCommercialMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= wal_CommercialAndIndustrialMember		 1,089us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_CommercialAndIndustrialCommercialMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= wal_CommercialAndIndustrialMember		 6,700us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_CommercialAndIndustrialCommercialMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= wal_CommercialAndIndustrialMember
Leases [Member] | Commercial and industrial [Member]      
Financing Receivable, Modifications [Line Items]      
Number of Loans 0us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_CommercialAndIndustrialLeasesMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= wal_CommercialAndIndustrialMember		 0us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_CommercialAndIndustrialLeasesMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= wal_CommercialAndIndustrialMember		 0us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_CommercialAndIndustrialLeasesMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= wal_CommercialAndIndustrialMember
Recorded Investment 0us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_CommercialAndIndustrialLeasesMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= wal_CommercialAndIndustrialMember		 0us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_CommercialAndIndustrialLeasesMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= wal_CommercialAndIndustrialMember		 0us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_CommercialAndIndustrialLeasesMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= wal_CommercialAndIndustrialMember
Construction [Member] | Construction and land development [Member]      
Financing Receivable, Modifications [Line Items]      
Number of Loans 0us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_ConstructionAndLandDevelopmentConstructionMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= wal_ConstructionAndLandDevelopmentLandMember		 0us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_ConstructionAndLandDevelopmentConstructionMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= wal_ConstructionAndLandDevelopmentLandMember		 0us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_ConstructionAndLandDevelopmentConstructionMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= wal_ConstructionAndLandDevelopmentLandMember
Recorded Investment 0us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_ConstructionAndLandDevelopmentConstructionMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= wal_ConstructionAndLandDevelopmentLandMember		 0us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_ConstructionAndLandDevelopmentConstructionMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= wal_ConstructionAndLandDevelopmentLandMember		 0us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wal_ConstructionAndLandDevelopmentConstructionMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= wal_ConstructionAndLandDevelopmentLandMember
Land [Member] | Construction and land development [Member]      
Financing Receivable, Modifications [Line Items]      
Number of Loans 0us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_LandMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= wal_ConstructionAndLandDevelopmentLandMember		 2us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_LandMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= wal_ConstructionAndLandDevelopmentLandMember		 5us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_LandMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= wal_ConstructionAndLandDevelopmentLandMember
Recorded Investment $ 0us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_LandMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= wal_ConstructionAndLandDevelopmentLandMember		 $ 330us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_LandMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= wal_ConstructionAndLandDevelopmentLandMember		 $ 4,013us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_LandMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= wal_ConstructionAndLandDevelopmentLandMember