Consolidated Statements Of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Statement of Other Comprehensive Income [Abstract]
Net income	$ 208,034	$ 206,650	$ 233,320
Other comprehensive income, net of tax:
Foreign currency translation adjustments	5,904	(3,195)	2,205
Unrealized holding loss on investments:
Unrealized holding gains during the period, net of income taxes of $86, $811 and $486	341	1,369	484
Other Comprehensive Income (Loss), Reclassification Adjustment for Sale of Securities Included in Net Income, Net of Income Taxes of $50, $77 and $56	(86)	(134)	(105)
Total other comprehensive income, net of tax	6,159	(1,960)	2,584
Comprehensive income	214,193	204,690	235,904
Comprehensive income attributable to the noncontrolling interest	(3,006)	(988)	(2,318)
Comprehensive income attributable to SEI Investments Company	$ 211,187	$ 203,702	$ 233,586