Debt Instrument, Term of Instrument

No definition available.

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Period Type:	instant

- Definition

Maximum borrowing capacity under the borrowing facility for letters of credit.

+ References

No definition available.

+ Details

Name:	asgn_LetterOfCreditMaximumBorrowingCapacity
Namespace Prefix:	asgn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The leverage ratio as defined in the credit agreement.

+ References

No definition available.

+ Details

Name:	asgn_LeverageRatio
Namespace Prefix:	asgn_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Line of Credit Facility, Increase in Additional Principal Amount

+ References

No definition available.

+ Details

Name:	asgn_LineOfCreditFacilityIncreaseInAdditionalPrincipalAmount
Namespace Prefix:	asgn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

+ References

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The stated principal amount of the debt instrument at time of issuance, which may vary from the carrying amount because of unamortized premium or discount.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 55

-Paragraph 8

-URI http://asc.fasb.org/extlink&oid=6584090&loc=d3e28878-108400

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 21

-Paragraph 16, 20

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Description of the frequency of periodic payments (monthly, quarterly, annual).

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 129

-Paragraph 2, 4

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 470

-Section 50

-Paragraph 3

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6479336&loc=d3e64711-112823

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_DebtInstrumentLineItems
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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of the required periodic payments including both interest and principal payments.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 470

-Section 50

-Paragraph 3

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6479336&loc=d3e64711-112823

+ Details

Name:	us-gaap_DebtInstrumentPeriodicPayment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 129

-Paragraph 2, 4

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 20, 22

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.16)

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.16)

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 16

-Article 9

+ Details

Name:	us-gaap_SecuredDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Long-Term Debt (Details) (USD $)	0 Months Ended		0 Months Ended							0 Months Ended													0 Months Ended
Long-Term Debt (Details) (USD $)	Sep. 30, 2012	Dec. 31, 2011	May 15, 2012 Maximum	May 15, 2012 Minimum	May 15, 2012 Leverage Ratio Greater Than or Equal to 3	May 15, 2012 Leverage Ratio Less Than 3 but Greater Than or Equal to 2	May 15, 2012 Leverage Ratio Less Than 2	Sep. 30, 2012 Term Loan Facility	Dec. 31, 2011 Term Loan Facility	May 15, 2012 Term Loan Facility $100 million term A loan facility, due May 2017	Sep. 30, 2012 Term Loan Facility $100 million term A loan facility, due May 2017	Dec. 31, 2011 Term Loan Facility $100 million term A loan facility, due May 2017	Sep. 30, 2012 Term Loan Facility $365 million term B loan facility, due May 2019	May 15, 2012 Term Loan Facility $365 million term B loan facility, due May 2019	Dec. 31, 2011 Term Loan Facility $365 million term B loan facility, due May 2019	May 15, 2012 Term Loan Facility $365 million term B loan facility, due May 2019 Eurodollar	May 15, 2012 Term Loan Facility $365 million term B loan facility, due May 2019 Base Rate	May 15, 2012 Term Loan Facility Revolving Loans and Term A Loans Eurodollar Maximum	May 15, 2012 Term Loan Facility Revolving Loans and Term A Loans Eurodollar Minimum	May 15, 2012 Term Loan Facility Revolving Loans and Term A Loans Base Rate Maximum	May 15, 2012 Term Loan Facility Revolving Loans and Term A Loans Base Rate Minimum	May 15, 2012 Term Loan Facility Senior Secured Credit Agreement	May 15, 2012 Term Loan Facility Senior Secured Credit Agreement Federal Funds Rate	May 15, 2012 Term Loan Facility Senior Secured Credit Agreement One-Month Eurodollar Rate	Sep. 30, 2012 Revolving Credit Facility	Dec. 31, 2011 Revolving Credit Facility	Sep. 30, 2012 Revolving Credit Facility $75 million revolving credit facility, due May 2017	May 15, 2012 Revolving Credit Facility $75 million revolving credit facility, due May 2017	Dec. 31, 2011 Revolving Credit Facility $75 million revolving credit facility, due May 2017	May 15, 2012 Revolving Credit Facility $75 million revolving credit facility, due May 2017 Letters of Credit
Debt Instrument [Line Items]
Senior Secured Debt	$ 439,088,000	$ 86,750,000						$ 0	$ 43,750,000		$ 95,000,000	$ 0	$ 334,088,000		$ 0										$ 0	$ 43,000,000	$ 10,000,000		$ 0
Face amount of term loan										100,000,000				365,000,000
Line of credit facility, maximum borrowing capacity																												75,000,000
Term of instrument										5 years				7 years														5 years
Letter of Credit, Maximum Borrowing Capacity																														15,000,000
Increase to borrowing capacity available under credit facility																						75,000,000
Description of variable rate basis																							federal funds rate	one-month Eurodollar rate
Basis spread on variable rate borrowings																3.75%	2.75%	3.25%	2.75%	2.25%	1.75%		0.50%	1.00%
Revolving credit facility, unused portion, commitment fee percentage					0.50%	0.40%	0.30%
Frequency of amortization payment										quarterly amortization payments
Quarterly amortization payments										$ 2,500,000
Leverage ratio	2.96		4.50	3.00