v2.4.0.6
Accumulated Comprehensive Income (Loss) (Schedule Of Accumulated Other Comprehensive Income (Loss), Net Of Tax) (Details) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended 6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Jun. 30, 2012
Jun. 30, 2011
Dec. 31, 2011
Accumulated Other Comprehensive Income [Line Items]          
Accumulated other comprehensive income (loss), Foreign Currency Translation Adjustments $ (456)   $ (456)   $ (674)
Accumulated other comprehensive income (loss), Unrealized Holding Gains (Losses) on Investments 2,593   2,593   2,574
Accumulated Other Comprehensive Income (Loss) 2,137   2,137   1,900
Total comprehensive loss, Foreign Currency Translation Adjustments (2,156) 1,467 547 4,295  
Total comprehensive loss, Unrealized Holding Gains (Losses) on Investments     19    
Total other comprehensive income, net of tax (2,108) 2,255 566 4,810  
Total comprehensive loss attributable to noncontrolling interest, Foreign Currency Translation Adjustments     (329) (925)  
Total comprehensive income attributable to noncontrolling interest, Unrealized Holding Gains (Losses) on Investments     0    
Total comprehensive loss attributable to noncontrolling interest     (329)    
Total comprehensive income attributable to SEI Investments Company, Foreign Currency Translation Adjustments     218    
Total comprehensive (loss) attributable to SEI Investments Company, Unrealized Holding Gains (Losses) on Investments     19    
Total comprehensive income attributable to SEI Investments Company     237    
SEI Investments Company [Member]
          
Accumulated Other Comprehensive Income [Line Items]          
Accumulated other comprehensive income (loss), Foreign Currency Translation Adjustments (1,496)   (1,496)   (2,043)
Accumulated other comprehensive income (loss), Unrealized Holding Gains (Losses) on Investments 2,593   2,593   2,574
Accumulated Other Comprehensive Income (Loss) 1,097   1,097   531
Noncontrolling Interest [Member]
          
Accumulated Other Comprehensive Income [Line Items]          
Accumulated other comprehensive income (loss), Foreign Currency Translation Adjustments 1,040   1,040   1,369
Accumulated other comprehensive income (loss), Unrealized Holding Gains (Losses) on Investments 0   0   0
Accumulated Other Comprehensive Income (Loss) $ 1,040   $ 1,040   $ 1,369