Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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The expense recognized in the current period that allocates the cost of nonproduction tangible assets over their useful lives.

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Composition of Certain Financial Statement Captions (Property And Equipment) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Property and Equipment, gross	$ 401,135		$ 401,135		$ 366,830
Less: Accumulated depreciation	(258,783)		(258,783)		(241,295)
Property and Equipment, net	142,352		142,352		125,535
Depreciation expense	6,108	$ 5,579	17,946	$ 16,494
Loss on write off of purchased software related to the SEI Wealth Platform			(6,055)	$ 0
Building [Member]
Property, Plant and Equipment [Line Items]
Property and Equipment, gross	151,037		151,037		149,890
Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and Equipment, gross	87,684		87,684		78,266
Land [Member]
Property, Plant and Equipment [Line Items]
Property and Equipment, gross	10,003		10,003		9,997
Purchased Software [Member]
Property, Plant and Equipment [Line Items]
Property and Equipment, gross	122,295		122,295		104,964
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and Equipment, gross	16,932		16,932		16,944
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and Equipment, gross	11,996		11,996		5,675
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property and Equipment, gross	$ 1,188		$ 1,188		$ 1,094
SEI Wealth Platform [Member]
Property, Plant and Equipment [Line Items]
Income statement classification for purchased software write off related to the SEI Wealth Platform	Facilities, supplies and other costs
SEI Wealth Platform [Member] \| Property, Plant and Equipment [Member]
Property, Plant and Equipment [Line Items]
Loss on write off of purchased software related to the SEI Wealth Platform	$ 522
Private Banks [Member] \| SEI Wealth Platform [Member]
Property, Plant and Equipment [Line Items]
Segment classification for purchased software write off related to the SEI Wealth Platform	Private Banks