Business Segment Information (Schedule Of Financial Information About Business Segments) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Segment Reporting Information [Line Items]
Revenues	$ 325,444us-gaap_Revenues	$ 302,386us-gaap_Revenues
Expenses	219,015us-gaap_OperatingCostsAndExpenses	212,295us-gaap_OperatingCostsAndExpenses
Operating profit (loss)	106,429us-gaap_GrossProfit	90,091us-gaap_GrossProfit
Gain on sale of subsidiary	2,791	5,582
Interest income	180us-gaap_InterestAndOtherIncome	0us-gaap_InterestAndOtherIncome
Total profit (loss)	109,400seic_TotalProfitLoss	95,673seic_TotalProfitLoss
Private Banks [Member]
Segment Reporting Information [Line Items]
Revenues	111,213	105,179
Expenses	99,256	100,190
Operating profit (loss)	11,957	4,989
Gain on sale of subsidiary	2,791	5,582
Interest income	180	0
Total profit (loss)	14,928	10,571
Investment Advisors [Member]
Segment Reporting Information [Line Items]
Revenues	74,015	66,424
Expenses	39,059	34,577
Operating profit (loss)	34,956	31,847
Gain on sale of subsidiary	0	0
Interest income	0	0
Total profit (loss)	34,956	31,847
Institutional Investors [Member]
Segment Reporting Information [Line Items]
Revenues	73,548	68,657
Expenses	35,211	34,095
Operating profit (loss)	38,337	34,562
Gain on sale of subsidiary	0	0
Interest income	0	0
Total profit (loss)	38,337	34,562
Investment Managers [Member]
Segment Reporting Information [Line Items]
Revenues	65,367	61,008
Expenses	40,623	39,184
Operating profit (loss)	24,744	21,824
Gain on sale of subsidiary	0	0
Interest income	0	0
Total profit (loss)	24,744	21,824
Investments In New Businesses [Member]
Segment Reporting Information [Line Items]
Revenues	1,301	1,118
Expenses	4,866	4,249
Operating profit (loss)	(3,565)	(3,131)
Gain on sale of subsidiary	0	0
Interest income	0	0
Total profit (loss)	$ (3,565)	$ (3,131)

Total profit (loss)

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- Definition

The gain (loss) resulting from the sale of a disposal group that is not a discontinued operation. It is included in income from continuing operations before income taxes in the income statement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 205

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6360339&loc=d3e1361-107760

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 360

-SubTopic 10

-Section 45

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=8077374&loc=d3e2443-110228

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- Definition

Aggregate revenue less cost of goods and services sold or operating expenses directly attributable to the revenue generation activity.

+ References

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- Definition

The amount of interest income and other income recognized during the period. Included in this element is interest derived from investments in debt securities, cash and cash equivalents, and other investments which reflect the time value of money or transactions in which the payments are for the use or forbearance of money and other income from ancillary business-related activities (that is, excluding major activities considered part of the normal operations of the business).

+ References

No definition available.

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- Definition

Generally recurring costs associated with normal operations except for the portion of these expenses which can be clearly related to production and included in cost of sales or services. Excludes Selling, General and Administrative Expense.

+ References

No definition available.

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- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Article 5

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