v2.4.0.6

Marketable Securities (Narrative) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Net unrealized holding gains	$ 2,593		$ 2,593		$ 2,574
Unrealized holding gains during the period, income tax expense			1,572		1,518
Available-for-sale Securities, Gross Realized Gain (Loss)			0	0
Net gain (loss) from investments	664	(1,948)	3,869	5,330
Securities owned	21,057		21,057		20,949
SEI Private Trust Company [Member]
Schedule of Available-for-sale Securities [Line Items]
Debt maturity, minimum	2020
Debt maturity, maximum	2041
U.S. Government Agency And Commercial Paper Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Debt maturity, maximum	one
SIV Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Net gains from SIV securities			3,954	4,920
Gains from cash payments received from SIV securities			4,463	6,232
Gains or losses from increase/decrease in fair value of SIV securities			$ (509)	$ (1,312)

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Gains from cash payments received from SIV securities.

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Unrealized Holding Gains During the Period, Income Tax Expense

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Accumulated appreciation or loss, net of tax, in value of the total of available-for-sale securities at the end of an accounting period.

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This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities.

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When presenting a range of maturity dates, the latest date when the outstanding debt instruments are required to be repaid. May be presented in a variety of ways (for example: year only, month and year, day, month and year, and number of years).

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The fair value as of the balance sheet date of firm holdings in debt obligations issued by the US government including short-term Treasury bills, medium-term Treasury notes, and long-term Treasury bonds, as well as debt issued by agencies. Includes both pledged (to counterparties as collateral for financing transactions) and unpledged holdings.

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This item represents the net total realized and unrealized gain (loss) included in earnings for the period as a result of selling or holding marketable securities categorized as trading, available-for-sale, or held-to-maturity, including the unrealized holding gain (loss) of held-to-maturity securities transferred to the trading security category and the cumulative unrealized gain (loss) which was included in other comprehensive income (a separate component of shareholders' equity) for available-for-sale securities transferred to trading securities during the period. Additionally, this item would include any gains (losses) realized during the period from the sale of investments accounted for under the cost method of accounting and losses recognized for other than temporary impairments (OTTI) of the subject investments.

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The increases or decreases in the market value of unsold securities whose gains or losses were included in earnings, and which, were not separately or otherwise categorized as trading, available-for-sale, or held-to-maturity.

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