Leverage ratio limit in latest year of debt facility, as described in debt agreement.

No definition available.

Name:	asgn_LeverageRatioinLatestYearofDebtTerm
Namespace Prefix:	asgn_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Line of Credit Facility, Increase in Additional Principal Amount

+ References

No definition available.

+ Details

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

- Definition

Pledged equity interest in foreign subsidiaries

+ References

No definition available.

+ Details

Name:	asgn_Pledgedequityinterestinforeignsubsidiaries
Namespace Prefix:	asgn_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

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

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ 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 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(1))

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

+ Details

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

- Definition

Minimum contractual interest rate for funds borrowed, under the debt agreement.

+ 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(a)(2))

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

+ Details

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

- Details

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

- Definition

Weighted average interest rate of debt outstanding.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtWeightedAverageInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
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

- Details

Name:	asgn_InterestRateTypeAxis=us-gaap_EurodollarMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=asgn_TermALoanFacilitydueMay2018Member
Namespace Prefix:
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- Details

Name:	us-gaap_DebtInstrumentAxis=asgn_TermBLoanFacilitydueMay2020Member
Namespace Prefix:
Data Type:	na
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- Details

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Namespace Prefix:
Data Type:	na
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- Details

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Long-Term Debt Long-term Debt text (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Jun. 30, 2015	May 16, 2013
Debt Instrument [Line Items]
Pledged equity interest in foreign subsidiaries	65.00%
Debt, Weighted Average Interest Rate	2.90%us-gaap_DebtWeightedAverageInterestRate
Term-A Loan Facility due May 2018 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate at Period End	2.20%
Term-B Loan Facility due May 2020 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate at Period End	3.50%
Eurodollar [Member] \| Term-B Loan Facility due May 2020 [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	2.50%
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Minimum	1.00%
Minimum [Member] \| Revolving Credit Facility due May 2018 [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.25%
Minimum [Member] \| Eurodollar Rate or Base Rate [Member] \| Revolving Loans and Term A Loans [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	1.75%
Maximum [Member]
Debt Instrument [Line Items]
Leverage Ratio in Latest Year of Debt Term	3,500.00	3.25
Maximum [Member] \| Revolving Credit Facility due May 2018 [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.40%
Maximum [Member] \| Eurodollar Rate or Base Rate [Member] \| Revolving Loans and Term A Loans [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	2.50%
Notes Payable to Banks [Member] \| Term A Loans, Term B Loans and Revolving Loans [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Increase in Additional Principal Amount			$ 100.0