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Line Of Credit (Details) (Line of Credit [Member], USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Line of Credit Facility [Line Items]      
Debt Instrument, Term 5 years    
Credit facility $ 300,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity    
Credit facility, expiration date Feb. 02, 2017    
Credit facility, commitment fee per annum on daily unused portion, percent 0.15%us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage    
Aggregate amount that may increase under credit facility 100,000seic_LineofCreditFacilityConditionalIncreaseDecreaseNet    
Credit Facility, commitment fees $ 458us-gaap_LineOfCreditFacilityCommitmentFeeAmount $ 458us-gaap_LineOfCreditFacilityCommitmentFeeAmount $ 585us-gaap_LineOfCreditFacilityCommitmentFeeAmount
London Interbank Offered Rate (LIBOR) [Member]
      
Line of Credit Facility [Line Items]      
Credit facility interest accrued, percentage above LIBOR 1.25%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_CreditFacilityAxis
= us-gaap_LineOfCreditMember
/ us-gaap_VariableRateAxis
= us-gaap_LondonInterbankOfferedRateLIBORMember