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Acquisitions Business Combinations (Policies) | 12 Months Ended
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Dec. 31, 2016
Business Combinations [Abstract] |
Acquisition [Policy Text Block] | Assets and liabilities of the acquired companies were recorded at their estimated fair values at the dates of acquisition. The excess purchase price over the fair value of net tangible assets and identifiable intangible assets acquired has been allocated to goodwill. The fair value assigned to identifiable intangible assets was determined primarily by using a discounted cash flow method.

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- Definition Acquisition [Policy Text Block] + References No definition available. + Details
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Namespace Prefix: | asgn_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
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Balance Type: | na
Period Type: | duration