Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 82,813	$ 83,494	$ 157,633	$ 155,764
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments	3,378	(1,800)	1,412	(7,107)
Unrealized gain (loss) on investments:
Unrealized gains during the period, net of income taxes of $(461), $(771), $(756) and $(812)	453	(1,361)	991	(1,240)
Less: reclassification adjustment for gains realized in net income, net of income taxes of $13, $(66), $38 and $(185)	(24)	(121)	(69)	(342)
Net unrealized gain (loss) on investments	429	(1,482)	922	(1,582)
Total other comprehensive income (loss), net of tax	3,807	(3,282)	2,334	(8,689)
Comprehensive income	86,620	80,212	159,967	147,075
Comprehensive loss attributable to the noncontrolling interest	0	0	0	101
Comprehensive income attributable to SEI Investments Company	$ 86,620	$ 80,212	$ 159,967	$ 147,176