Marketable Securities (Investments Available For Sale) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Investment Available for Sale, Cost Amount	$ 71,486	$ 78,916
Investment Available for Sale, Gross Unrealized Gains	4,396	4,452
Investment Available for Sale, Gross Unrealized Losses	(13)	(360)
Investment Available for Sale, Fair Value	75,869	83,008
SEI-Sponsored Mutual Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Investment Available for Sale, Cost Amount	12,953	8,243
Investment Available for Sale, Gross Unrealized Gains	376	48
Investment Available for Sale, Gross Unrealized Losses	(13)	(360)
Investment Available for Sale, Fair Value	13,316	7,931
Equity Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Investment Available for Sale, Cost Amount	2,610	69
Investment Available for Sale, Gross Unrealized Gains	0	10
Investment Available for Sale, Gross Unrealized Losses	0	0
Investment Available for Sale, Fair Value	2,610	79
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Investment Available for Sale, Cost Amount	55,923	70,604
Investment Available for Sale, Gross Unrealized Gains	4,020	4,394
Investment Available for Sale, Gross Unrealized Losses	0	0
Investment Available for Sale, Fair Value	$ 59,943	$ 74,998

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

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- Definition

Investments in debt and equity securities which are categorized neither as held-to-maturity nor trading and which are intended to be sold or mature more than one year from the balance sheet date or operating cycle, if longer. Such securities are reported at fair value; unrealized gains (losses) related to Available-for-sale Securities are excluded from earnings and reported in a separate component of shareholders' equity (other comprehensive income), unless the Available-for-sale security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding gain (loss) of an Available-for-sale security that is designated as being hedged in a fair value hedge is recognized in earnings during the period of the hedge, as are other than temporary declines in fair value below the cost basis for investments in equity securities and debt securities that an entity intends to sell or it is more likely than not that it will be required to sell before the recovery of its amortized cost basis. Other than temporary declines in fair value below the cost basis for debt securities categorized as Available-for-sale that an entity does not intend to sell and for which it is not more likely than not that the entity will be required to sell before the recovery of its amortized cost basis are bifurcated into credit losses and losses related to all other factors. Other than temporary declines in fair value below cost basis related to credit losses are recognized in earnings, and losses related to all other factors are recognized in other comprehensive income.

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

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

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Reference 6: http://www.xbrl.org/2003/role/presentationRef

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