Rights received by common shareholder for each common share outstanding, rights.

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- Definition

Rights non-voting, redeemable days.

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No definition available.

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Number of days, rights become exercisable following public announcement.

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- Definition

Common shares received by holders upon surrender of rights, percentage.

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- Definition

Right redeemable price, per right.

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Securities and assets of equivalent value, purchase price, per unit

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Rights Agreement, Triggering Event Voting Interest

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- Definition

Share Based Compensation Arrangement By Share Based Payment Award, Market Paid Price Offering Date

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No definition available.

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- Definition

Aggregate dividends paid during the period for each share of common stock outstanding.

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Aggregate dividends declared during the period for each share of common stock outstanding.

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- Definition

Amount of paid and unpaid cash, stock, and paid-in-kind (PIK) dividends declared, for example, but not limited to, common and preferred stock.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

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-SubTopic 405

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- Definition

Amount of paid and unpaid common stock dividends declared with the form of settlement in cash, stock and payment-in-kind (PIK).

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- Definition

Unrecognized cost of unvested share-based compensation awards.

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-Publisher FASB

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

Face amount or stated value per share of preferred stock nonredeemable or redeemable solely at the option of the issuer.

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-Publisher FASB

-Name Accounting Standards Codification

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-Subparagraph (SX 210.5-02.28)

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-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 29

-Article 5

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- Definition

Additional share-based compensation cost recognized as a result of an occurrence of an event that accelerates its recognition.

+ References

No definition available.

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- Definition

Percentage of vesting of share-based compensation awards.

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- Definition

Date the equity-based award expires, in CCYY-MM-DD format.

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- Definition

The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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-Paragraph 2

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- Definition

Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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- Definition

The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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-Publisher FASB

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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- Definition

Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

Price of a single share of a number of saleable stocks of a company.

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No definition available.

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- Definition

Number of shares issued during the period as a result of an employee stock purchase plan.

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Amount remaining of a stock repurchase plan authorized.

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Shareholders' Equity (Narrative) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	0 Months Ended				12 Months Ended			0 Months Ended
	Dec. 09, 2014	Jun. 24, 2014	May 21, 2014	Dec. 28, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jan. 06, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average fair value of stock options granted					$ 10.88	$ 10.45	$ 6.73
Change in management estimate of stock-based compensation expense amortization						$ 19,637
Unrecognized compensation cost					45,115
Weighted average period for recognition of unrecognized compensation cost					2 years 5 months 12 days
Total options that were exercisable					10,295,000	14,601,000	9,760,000
Options outstanding weighted average remaining contractual life, years					5 years 9 months 15 days
Total intrinsic value of options exercised					83,196	47,392
Aggregate intrinsic value of options exercisable					200,328
Total intrinsic value of options outstanding					302,441
Share price of SEI common stock					$ 40.04us-gaap_SharePrice
Rights received by common shareholder for each common share outstanding, rights					1
Series A Junior Participating Preferred stock, par value					$ 0.05	$ 0.05
Securities and assets of equivalent value, purchase price, per unit					$ 150
Number of days, rights become exercisable following public announcement					0 years 0 months 10 days
Acquiring Person, beneficial ownership of the outstanding common stock, minimum percentage					20.00%
Common shares received by holders upon surrender of rights, percentage					50.00%
Rights non-voting, redeemable days					0 years 0 months 10 days
Right redeemable price, per right					0.01
Dividends declared per common share	$ 0.24		$ 0.22		$ 0.46	$ 0.42	$ 0.63
Dividends paid per common share		$ 0.22
Dividends declared				55,149us-gaap_DividendsCommonStock	77,158us-gaap_DividendsCommonStock	71,665us-gaap_DividendsCommonStock	108,817us-gaap_DividendsCommonStock
Dividends paid				55,149us-gaap_Dividends
Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividends paid per common share								$ 0.24
Common Stock Buyback [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining stock repurchase authorization amount					$ 102,713
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration date for options outstanding					Dec. 14, 2015
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration date for options outstanding					Dec. 09, 2024
2014 Equity Compensation Plan [Member] \| Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rate					50.00%
2014 Equity Compensation Plan [Member] \| Tranche Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rate					50.00%
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee stock purchase plan, employee eligible percentage on offerings of common stock					85.00%
Shares reserved under the plan					15,600,000
Issuance of common stock under the employee stock purchase plan, shares					11,732,000