FAIR VALUE (Details 4) (Discount cash flow)	9 Months Ended
Sep. 30, 2012
Derivative Payable \| Low end of range
Quantitative unobservable assumptions
Credit Risk Adjustment	0.30%
Derivative Payable \| High end of range
Quantitative unobservable assumptions
Credit Risk Adjustment	1.96%
Trust Preferred Securities
Quantitative unobservable assumptions
Constant prepayment rate for year 1-5	0.00%
Constant prepayment rate, thereafter	1.00%
Constant default rate for year 1-5	1.20%
Constant default rate, thereafter	0.75%
Recovery rate, existing deferral/defaults	0.00%
Recovery rate, future deferral	15.00%
Recovery period, future deferral	60 months

Credit risk adjustment rate used as an input to measure fair value.

No definition available.

Name:	ewbc_FairValueInputsCreditRiskAdjustmentRate
Namespace Prefix:	ewbc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of likelihood the underlying collateral will not be repaid and instead default, used as an input to measure fair value after five years.

+ References

No definition available.

+ Details

Name:	ewbc_FairValueInputsDefaultRateAfterFiveYears
Namespace Prefix:	ewbc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of likelihood the underlying collateral will not be repaid and instead default, used as an input to measure fair value for first five years.

+ References

No definition available.

+ Details

Name:	ewbc_FairValueInputsDefaultRateForFirstFiveYears
Namespace Prefix:	ewbc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Rate at which the underlying collateral is expected to prepay, used as an input to measure fair value after five years.

+ References

No definition available.

+ Details

Name:	ewbc_FairValueInputsPrepaymentRateAfterFiveYears
Namespace Prefix:	ewbc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Rate at which the underlying collateral is expected to prepay, used as an input to measure fair value for first five years.

+ References

No definition available.

+ Details

Name:	ewbc_FairValueInputsPrepaymentRateForFirstFiveYears
Namespace Prefix:	ewbc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Period at which the underlying collateral is expected to recover, used as an input to measure fair value.

+ References

No definition available.

+ Details

Name:	ewbc_FairValueInputsRecoveryPeriodForFutureDeferral
Namespace Prefix:	ewbc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Rate at which the underlying collateral is expected to recover for the existing deferrals, used as an input to measure fair value.

+ References

No definition available.

+ Details

Name:	ewbc_FairValueInputsRecoveryRateForExistingDeferral
Namespace Prefix:	ewbc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Rate at which the underlying collateral is expected to recover for future deferrals, used as an input to measure fair value.

+ References

No definition available.

+ Details

Name:	ewbc_FairValueInputsRecoveryRateForFutureDeferral
Namespace Prefix:	ewbc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration