XML 49 R97.htm IDEA: XBRL DOCUMENT v2.4.1.9
Stockholders' Equity - Additional Information (Detail) (USD $)
 1 Months Ended 3 Months Ended 12 Months Ended
Sep. 27, 2011
Jun. 30, 2013
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Weighted Average Share Price     $ 25.96wal_WeightedAverageSharePrice    
Proceeds from Issuance of Common Stock     $ 14,200,000wal_ProceedsfromIssuanceofCommonStockGross    
Offering Costs From Issuance Of Common Stock     500,000wal_OfferingCostsFromIssuanceOfCommonStock    
Proceeds from issuance of non-cumulative preferred stock 141,000,000us-gaap_PreferredStockValue   70,500,000us-gaap_PreferredStockValue 141,000,000us-gaap_PreferredStockValue  
Preferred stock, shares issued 141,000us-gaap_PreferredStockSharesIssued   141,000us-gaap_PreferredStockSharesIssued 141,000us-gaap_PreferredStockSharesIssued  
Par value of per share $ 0.0001us-gaap_PreferredStockParOrStatedValuePerShare   $ 0.0001us-gaap_PreferredStockParOrStatedValuePerShare $ 0.0001us-gaap_PreferredStockParOrStatedValuePerShare  
Liquidation per share $ 1,000us-gaap_PreferredStockLiquidationPreference   $ 1,000us-gaap_PreferredStockLiquidationPreference $ 1,000us-gaap_PreferredStockLiquidationPreference  
Dividend rate 5.00%us-gaap_PreferredStockDividendRatePercentage   1.00%us-gaap_PreferredStockDividendRatePercentage    
Common stock, issued     88,691,249us-gaap_CommonStockSharesIssued 87,186,403us-gaap_CommonStockSharesIssued  
Common stock, per value     $ 0.0001us-gaap_CommonStockParOrStatedValuePerShare $ 0.0001us-gaap_CommonStockParOrStatedValuePerShare  
Common stock, net value     9,000us-gaap_CommonStockValue 9,000us-gaap_CommonStockValue  
Number of shares authorized for grant     6,500,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized    
Stock awards grant     1,900,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant    
Maximum number of shares available for issuance   2,000,000.000000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized      
Maximum number of shares of stock that can be awarded to any person eligible   300,000.000000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumNumberOfSharesPerEmployee      
Preferred Stock [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Redeemed preference shares     70,500us-gaap_StockRedeemedOrCalledDuringPeriodShares
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_PreferredStockMember		    
Restricted stock awards [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Vesting period, years     3 years    
Nonvested [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Unvested share-based compensation arrangements     8,400,000us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions
/ us-gaap_AwardTypeAxis
= wal_NonvestedMember		    
Unvested share-based compensation arrangements, weighted average period     1 year 11 months 15 days 1 year 9 months 22 days 1 year 9 months 18 days
Unvested share-based compensation arrangements, intrinsic value     7,100,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue
/ us-gaap_AwardTypeAxis
= wal_NonvestedMember		 2,800,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue
/ us-gaap_AwardTypeAxis
= wal_NonvestedMember		 900,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue
/ us-gaap_AwardTypeAxis
= wal_NonvestedMember
Unvested share-based compensation arrangements, weighted average value     13,300,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue
/ us-gaap_AwardTypeAxis
= wal_NonvestedMember		 6,800,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue
/ us-gaap_AwardTypeAxis
= wal_NonvestedMember		 3,800,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue
/ us-gaap_AwardTypeAxis
= wal_NonvestedMember
Unvested share-based compensation arrangements, grant date fair value     $ 12,200,000wal_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodAggregateIntrinsicValue
/ us-gaap_AwardTypeAxis
= wal_NonvestedMember		 $ 6,700,000wal_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodAggregateIntrinsicValue
/ us-gaap_AwardTypeAxis
= wal_NonvestedMember		 $ 5,900,000wal_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodAggregateIntrinsicValue
/ us-gaap_AwardTypeAxis
= wal_NonvestedMember
Minimum          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Dividend rate 1.00%us-gaap_PreferredStockDividendRatePercentage
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		        
Maximum          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Dividend rate 9.00%us-gaap_PreferredStockDividendRatePercentage
/ us-gaap_RangeAxis
= us-gaap_MaximumMember