Consolidated Statements Of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Statement of Comprehensive Income [Abstract]
Net income	$ 67,195	$ 51,086	$ 222,959	$ 151,060
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments	3,146	3,464	(3,961)	4,011
Unrealized holding loss on investments:
Unrealized holding gains (losses) during the period, net of income taxes	354	586	(886)	642
Other comprehensive income (loss), reclassification adjustment for sale of securities included in net income, net of tax	55	10	(287)	(27)
Unrealized holding gain (loss) on investments:	409	596	(1,173)	615
Total other comprehensive income (loss), net of tax	3,555	4,060	(5,134)	4,626
Comprehensive income	70,750	55,146	217,825	155,686
Comprehensive (income) loss attributable to the noncontrolling interest	0	(847)	101	(1,630)
Comprehensive income attributable to SEI Investments Company	$ 70,750	$ 54,299	$ 217,926	$ 154,056