Consolidated Statements Of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Revenues:
Asset management, administration and distribution fees	$ 723,630	$ 669,788	$ 628,535
Information processing and software servicing fees	236,190	222,417	231,529
Transaction-based and trade execution fees	32,702	37,522	40,771
Total revenues	992,522	929,727	900,835
Expenses:
Subadvisory, distribution and other asset management costs	106,048	103,134	101,722
Software royalties and other information processing costs	26,722	27,437	24,419
Brokerage commissions	23,889	27,022	28,882
Compensation, benefits and other personnel	335,296	289,445	269,165
Stock-based compensation	15,736	14,112	26,783
Consulting, outsourcing and professional fees	109,828	113,171	89,033
Data processing and computer related	46,617	47,003	41,064
Facilities, supplies and other costs	60,976	55,579	56,284
Amortization	33,258	27,288	24,048
Depreciation	22,586	21,471	21,902
Total Expenses	780,956	725,662	683,302
Income from operations	211,566	204,065	217,533
Net gain from investments	14,067	3,360	48,533
Interest and dividend income	5,696	5,829	6,326
Interest expense	(504)	(585)	(1,478)
Other expense, net	0	0	(590)
Equity in earnings of unconsolidated affiliates	98,671	105,818	99,457
Net income before income taxes	329,496	318,487	369,781
Income taxes	121,462	111,837	136,461
Net income	208,034	206,650	233,320
Less: Net income attributable to the noncontrolling interest	(1,186)	(1,691)	(1,633)
Net income attributable to SEI Investments Company	$ 206,848	$ 204,959	$ 231,687
Basic earnings per common share	$ 1.19	$ 1.12	$ 1.23
Basic earnings per common share, shares	174,295	182,547	188,468
Diluted earnings per common share	$ 1.18	$ 1.11	$ 1.22
Diluted earnings per common share, shares	175,872	184,127	190,321
Dividends declared per common share	$ 0.63	$ 0.27	$ 0.20