Income Taxes (Deferred Tax Assets And Liabilities) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Allowance for doubtful accounts	$ 2,027	$ 1,716
Employee related accruals	7,240	6,442
State taxes	473	555
Workers’ compensation and medical malpractice loss reserves	4,068	4,767
Other	5,259asgn_DeferredTaxAssetsOtherCurrent	4,050asgn_DeferredTaxAssetsOtherCurrent
Current	19,067	17,530
Intangibles	(59,226)	(49,763)
Depreciation expense	(13,405)	(6,574)
Stock-based compensation	3,022	3,761
Net operating loss carryforwards	1,260	1,612
Other	1,554asgn_DeferredTaxAssetsOtherNoncurrent	1,869asgn_DeferredTaxAssetsOtherNoncurrent
Deferred Tax Liabilities, Gross, Noncurrent	(66,795)	(49,095)
Valuation allowance	(1,114)	(1,511)
Total deferred income tax assets (liabilities)	$ (48,842)us-gaap_DeferredTaxLiabilities	$ (33,076)us-gaap_DeferredTaxLiabilities

Deferred Tax Assets, Operating Loss Carryforwards, Noncurrent

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Deferred Tax Assets, Other, Current

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Amount after allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards, net of deferred tax liability attributable to taxable temporary differences expected to be realized or consumed within one year or operating cycle, if longer.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible state and local operating loss carryforwards.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from share-based compensation.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from accrued liabilities.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from the allowance for doubtful accounts.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from loss reserves other than estimated credit losses.

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Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.

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Amount of deferred tax liability attributable to taxable temporary differences net of deferred tax asset attributable to deductible temporary differences and carryforwards after valuation allowances.

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Amount of deferred tax liability attributable to taxable temporary differences from intangible assets other than goodwill.

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Gross amount of noncurrent deferred tax liabilities, which result from applying the applicable tax rate to taxable temporary differences pertaining to each jurisdiction to which the entity is obligated to pay income tax.

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Amount of deferred tax liability attributable to taxable temporary differences from property, plant, and equipment.

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