Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Current Assets:
Receivables, allowance for doubtful accounts	$ 625	$ 805
Property and Equipment, accumulated depreciation	214,653	201,418
Capitalized Software, accumulated amortization	$ 171,015	$ 149,747
SEI Investments shareholders' equity:
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	750,000	750,000
Common stock, shares issued	170,500	172,220
Common stock, shares outstanding	170,500	172,220