Contractual Quarterly Payments

No definition available.

Name:	asgn_ContractualQuarterlyPayments
Namespace Prefix:	asgn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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

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

+ References

No definition available.

+ Details

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

- Definition

Payments on Debt

+ References

No definition available.

+ Details

Name:	asgn_PaymentsonDebt
Namespace Prefix:	asgn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- 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

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: 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=34725769&loc=d3e28878-108400

Reference 2: 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

+ Details

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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ 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

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ 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 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
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 amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: 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 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 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 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 20, 22
-Article 5

+ Details

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

- 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 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 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 SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 19, 20, 22
-Article 5

+ Details

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

- Definition

The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

+ 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 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_UnamortizedDebtIssuanceExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=asgn_A825MillionTermBLoanFacilityand150MillionRevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=asgn_A150MillionRevolvingCreditFacilityDueJune2020Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=asgn_A825MillionTermBLoanFacilitydueJune2022Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=asgn_A125millionrevolvingcreditfacilityrepaidJune2015Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=asgn_TermALoanFacilityrepaidJune2015Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=asgn_TermBLoanFacilityrepaidJune2015Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_NotesPayableToBanksMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Long-Term Debt (Details) $ in Thousands	1 Months Ended	12 Months Ended
Long-Term Debt (Details) $ in Thousands	Jun. 15, 2015 Rate	Dec. 31, 2015 USD ($)	Jun. 05, 2015 USD ($)	Dec. 31, 2014 USD ($)
Debt Instrument [Line Items]
Secured Debt		$ 774,000		$ 415,125
Unamortized Debt Issuance Expense		(18,492)		(3,268)
Long-term Debt		$ 755,508		411,857
Weighted average interest rate		3.68%
Contractual Quarterly Payments		$ 2,100
Payments on Debt		$ 101,000
Leverage ratio		3.02
Maximum [Member]
Debt Instrument [Line Items]
Leverage ratio		4.50
Leverage Ratio in Latest Year of Debt Term		3.25
$825 Million Term B Loan Facility and $150 Million Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Face amount of term loan			$ 975,000
$150 Million Revolving Credit Facility, Due June 2020 [Member]
Debt Instrument [Line Items]
Secured Debt		$ 50,000		0
Face amount of term loan			150,000
$825 Million Term B Loan Facility, due June 2022 [Member]
Debt Instrument [Line Items]
Secured Debt		724,000		0
Face amount of term loan			$ 825,000
$125 million revolving credit facility, repaid June 2015 [Member]
Debt Instrument [Line Items]
Secured Debt		0		76,000
Term-A Loan Facility repaid June 2015 [Member]
Debt Instrument [Line Items]
Secured Debt		0		158,813
Term-B Loan Facility repaid June 2015 [Member]
Debt Instrument [Line Items]
Secured Debt		0		$ 180,312
Term Loan Facility \| $150 Million Revolving Credit Facility, Due June 2020 [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Basis spread on variable rate borrowings \| Rate	2.50%
Revolving credit facility, unused portion, commitment fee percentage \| Rate	0.00%
Term Loan Facility \| $150 Million Revolving Credit Facility, Due June 2020 [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Basis spread on variable rate borrowings \| Rate	0.75%
Revolving credit facility, unused portion, commitment fee percentage \| Rate	0.00%
Term Loan Facility \| $825 Million Term B Loan Facility, due June 2022 [Member] \| Eurodollar [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Basis spread on variable rate borrowings \| Rate	3.00%
Revolving Credit Facility
Debt Instrument [Line Items]
Line of Credit Facility, Remaining Borrowing Capacity		$ 96,500