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Acquisitions Business Combinations Additional Information (Details) - USD ($) $ in Millions |  |  | 3 Months Ended |
--- | --- | --- | --- | ---
Jan. 25, 2019 | Apr. 02, 2018 | Mar. 31, 2019 | Mar. 31, 2018 | Dec. 31, 2018
Business Acquisition [Line Items] |  |  |  |  |
Cash paid for acquisitions, net of cash acquired |  |  | $ 48.8 | $ 0.0 |
Goodwill |  |  | $ 1,445.5 |  | $ 1,421.1
DHA |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |
Business Acquisition, Effective Date of Acquisition | Jan. 25, 2019 |  |  |  |
Business Acquisition, Name of Acquired Entity | DHA Group, Inc. |  |  |  |
Business Acquisition, Description of Acquired Entity | headquartered in Washington, D.C. |  |  |  |
Working capital excess of target working capital | $ 2.8 |  |  |  |
ECS |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |
Business Acquisition, Effective Date of Acquisition |  | Apr. 02, 2018 |  |  |
Business Acquisition, Name of Acquired Entity |  | ECS Federal, LLC |  |  |
Business Acquisition, Description of Acquired Entity |  | headquartered in Fairfax, Virginia |  |  |
Payments to Acquire Businesses, Gross |  | $ 775.0 |  |  |
Business Combination, Reason for Business Combination |  | The ECS acquisition allows the Company to compete in the Federal IT and professional services sector. |  |  |
Goodwill |  | $ 528.2 |  |  |
Business Acquisition, Goodwill, Expected Tax Deductible Amount |  | 514.2 |  |  |
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets |  | $ 195.0 |  |  |
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life |  | 11 years |  |  |

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- Definition Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16265-109275 + Details
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- Definition With respect to a business combination completed during the period, this element provides a description of the business, other than the name, which may include the industry, size, products and other important information. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463 + Details
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- Definition Date when the acquirer obtains control of the acquiree, in CCYY-MM-DD format. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 25 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=84229725&loc=d3e848-128460 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 25 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=84229725&loc=d3e845-128460 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463 + Details
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- Definition The amount of goodwill arising from a business combination that is expected to be deductible for tax purposes. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479 + Details
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- Definition This element represents a description of the primary reason for the business combination which may consist of general categories such as top-line growth, synergistic benefits, market share, and diversification and the more detailed factors that might apply. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463 + Details
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- Definition Amount of assets, excluding financial assets and goodwill, that lack physical substance, having a projected indefinite period of benefit, acquired at the acquisition date. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84161108&loc=d3e4845-128472 + Details
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- Definition Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=99380562&loc=d3e13770-109266 + Details
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- Definition The cash outflow associated with the acquisition of a business, net of the cash acquired from the purchase. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 13 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3213-108585 + Details
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