Derivatives ((Losses) in Foreign Currency Translation Adjustment) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Derivative instruments designated as hedging instruments \| Net investment hedges \| Foreign exchange swap contracts
Derivative [Line Items]
Losses recognized in AOCI	$ 2,005	$ 1,154

Other comprehensive income (loss) on derivatives instrument designated and qualifying in Net Investment Hedge, Before Tax, Period Increase (Decrease).

No definition available.

Name:	ewbc_OtherComprehensiveIncomeLossNetInvestmentHedgeGainLossBeforeTax
Namespace Prefix:	ewbc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration