ASGN (ASGN) 10-Q 9 Nov 18 2018 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Oct. 31, 2018
Entity Information [Line Items]
Entity Registrant Name	ASGN Incorporated
Entity Central Index Key	890,564
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		52,477,027

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 40,888	$ 36,667
Accounts receivable, net	572,864	428,536
Prepaid expenses and income taxes	13,606	18,592
Workers' compensation receivable	14,890	12,702
Other current assets	4,351	3,026
Total current assets	646,599	499,523
Property and equipment, net	81,672	57,996
Identifiable intangible assets, net	502,557	352,766
Goodwill	1,420,636	894,095
Other non-current assets	13,126	5,749
Total assets	2,664,590	1,810,129
Current liabilities:
Accounts payable	28,921	6,870
Accrued payroll and contract professional pay	195,698	114,832
Workers’ compensation loss reserves	17,137	14,777
Income taxes payable	8,180	1,229
Other current liabilities	41,481	29,009
Total current liabilities	291,417	166,717
Long-term debt	1,154,154	575,213
Deferred income tax liabilities	71,712	69,436
Other long-term liabilities	17,483	7,372
Total liabilities	1,534,766	818,738
Commitments and contingencies (Note 7)
Stockholders’ equity:
Preferred Stock, Value, $0.01 par value	0	0
Common stock, $0.01 par value	524	521
Paid-in capital	594,123	566,090
Retained earnings	540,244	428,419
Accumulated other comprehensive loss	(5,067)	(3,639)
Total stockholders’ equity	1,129,824	991,391
Total liabilities and stockholders’ equity	$ 2,664,590	$ 1,810,129

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Sep. 30, 2018	Dec. 31, 2017
Stockholders’ equity:
Preferred Stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred Stock, shares authorized (in shares)	1,000,000	1,000,000
Preferred Stock, shares issued (in shares)	0	0
Preferred Stock, shares outstanding (in shares)	0	0
Common Stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common Stock, shares authorized (in shares)	75,000,000	75,000,000
Common Stock, shares issued (in shares)	52,456,886	52,151,538
Common Stock: shares outstanding (in shares)	52,456,886	52,151,538

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenues	$ 906,449	$ 667,048	$ 2,470,131	$ 1,946,889
Cost of services	636,277	448,733	1,718,376	1,317,493
Gross profit	270,172	218,315	751,755	629,396
Selling, general and administrative expenses	177,335	149,197	521,395	440,446
Amortization of intangible assets	18,540	8,248	44,689	25,011
Operating income	74,297	60,870	185,671	163,939
Interest expense	(14,606)	(7,099)	(41,724)	(21,667)
Income before income taxes	59,691	53,771	143,947	142,272
Provision for income taxes	10,474	18,892	31,889	51,775
Income from continuing operations	49,217	34,879	112,058	90,497
Loss from discontinued operations, net of income taxes	(45)	(23)	(233)	(153)
Net income	$ 49,172	$ 34,856	$ 111,825	$ 90,344
Earnings per share:
Basic	$ 0.94	$ 0.66	$ 2.14	$ 1.72
Diluted	$ 0.93	$ 0.66	$ 2.11	$ 1.70
Number of shares and share equivalents used to calculate earnings per share:
Basic	52,362	52,500	52,282	52,660
Diluted	53,034	53,173	52,990	53,319
Reconciliation of net income to comprehensive income:
Net income	$ 49,172	$ 34,856	$ 111,825	$ 90,344
Foreign currency translation adjustment	(268)	1,783	(1,428)	5,628
Comprehensive income	$ 48,904	$ 36,639	$ 110,397	$ 95,972

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash Flows from Operating Activities:
Net income	$ 111,825	$ 90,344
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	71,298	43,493
Stock-based compensation	22,380	17,943
Provision for accounts receivable allowances	2,133	9,216
Workers’ compensation provision	2,459	2,383
Other	13,046	5,967
Changes in operating assets and liabilities:
Accounts receivable	(47,819)	(51,936)
Prepaid expenses and income taxes	12,482	(958)
Accounts payable	9,892	(135)
Accrued payroll and contract professional pay	26,942	14,291
Income taxes payable	6,849	13,426
Workers’ compensation loss reserves	(2,287)	(1,952)
Other	(5,639)	(3,895)
Net Cash Provided by Operating Activities	223,561	138,187
Cash Flows from Investing Activities:
Cash paid for property and equipment	(22,093)	(18,038)
Cash paid for acquisitions, net of cash acquired	(760,253)	(25,828)
Other	(180)	0
Net cash used in investing activities	(782,526)	(43,866)
Cash Flows from Financing Activities:
Principal payments of long-term debt	(231,000)	(69,500)
Proceeds from long-term debt	822,000	37,000
Debt issuance and amendment costs	(22,450)	(3,273)
Proceeds from option exercises and employee stock purchase plan	9,342	7,690
Payment of employment taxes related to release of restricted stock awards	(4,402)	(7,785)
Repurchase of common stock	0	(58,949)
Other	(9,473)	0
Net Cash provided by (used in) Financing Activities	564,017	(94,817)
Effect of exchange rate changes on cash and cash equivalents	(831)	1,429
Net Increase (Decrease) in Cash and Cash Equivalents	4,221	933
Cash and Cash Equivalents at Beginning of Year	36,667	27,044
Cash and Cash Equivalents at End of Period	40,888	27,977
Supplemental Disclosure of Cash Flow Information:
Income taxes	10,184	37,716
Interest	37,828	18,980
Supplemental Disclosure of Non-Cash Transactions:
Unpaid portion of additions to property and equipment	1,676	2,063
Unsettled repurchases of common stock	$ 0	$ 1,074

Financial Statement Presentatio

Financial Statement Presentation (Notes)	9 Months Ended
	Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Financial Statement Presentation	1. Financial Statement Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America ("GAAP") and the rules of the Securities and Exchange Commission (the "SEC"). Certain information and note disclosures normally included in annual financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to those rules and regulations. The December 31, 2017 condensed consolidated balance sheet was derived from audited financial statements. The financial statements include adjustments consisting of normal recurring items, which, in the opinion of management, are necessary for a fair presentation of the financial position of ASGN Incorporated and its subsidiaries ("ASGN" or the "Company") and its results of operations for the interim dates and periods set forth herein. The results for any of the interim periods are not necessarily indicative of the results to be expected for the full year or any other period. This Quarterly Report on Form 10-Q should be read in conjunction with the Company’s Annual Report on Form 10-K for the year ended December 31, 2017 .

Accounting Standards Update (No

Accounting Standards Update (Notes)	9 Months Ended
	Sep. 30, 2018
Accounting Changes and Error Corrections [Abstract]
Accounting Standards Update	2. Accounting Standards Update Recently Adopted Accounting Pronouncements Effective January 1, 2018, the Company adopted Accounting Standards Update ("ASU") No. 2014-09, Revenue from Contracts with Customers (Topic 606) , using the modified retrospective method. This update outlined a comprehensive new revenue recognition model designed to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The new standard also required additional quantitative and qualitative disclosures (see Note 3. Revenues ). Accounting Pronouncements Not Yet Adopted In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) , which is intended to improve financial reporting about leasing transactions. This standard requires a lessee to record the assets and liabilities for the rights and obligations created by lease terms of more than 12 months. As allowed by subsequently issued guidance, the Company expects to adopt the new leases standard on January 1, 2019, instead of the beginning of the earliest period presented. The Company expects to recognize right-of-use assets and lease liabilities on its balance sheet primarily for its real estate operating leases. The Company does not expect the standard will have a material impact on its results of operations or cash flows. The adoption of the standard will have no impact to the Company's debt covenants compliance under its current credit facility. In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement , which modifies the disclosure requirements on fair value measurements. The amendments in this update are effective for interim and annual periods for the Company beginning on January 1, 2020, with early adoption permitted. The Company is evaluating the effects that the adoption of this guidance will have on its disclosures. In August 2018, the FASB issued ASU No. 2018-15, Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract. The amendments in this update align the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software (and hosting arrangements that include an internal-use software license). The amendments in this update are effective for interim and annual periods for the Company beginning on January 1, 2020, with early adoption permitted. The amendments in this update may be applied either retrospectively or prospectively. The Company is in the process of evaluating the impact the standard will have on its consolidated financial statements. In November 2018, the FASB issued ASU No. 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction Between Topic 808 and Topic 606. The amendments in this update provide guidance on how to assess whether certain transactions between collaborative arrangement participants should be accounted for within the revenue recognition standard. The amendments in this update are effective for interim and annual periods for the Company beginning on January 1, 2020, with early adoption permitted. The Company is in the process of evaluating the impact the standard will have on its consolidated financial statements. In August 2018, the SEC adopted the final rule under SEC Release No. 33-10532, Disclosure Update and Simplification , amending certain disclosure requirements that were redundant, duplicative, overlapping, outdated or superseded. In addition, the amendments expanded the disclosure requirements on the analysis of stockholders' equity for interim financial statements. Under the amendments, an analysis of changes in each caption of stockholders' equity presented in the balance sheet at interim reporting periods must be provided in a note or separate statement. The analysis should present a reconciliation of the beginning balance to the ending balance of each period for which a statement of comprehensive income is presented. The Company plans to include this presentation of interim changes in stockholders' equity in its Quarterly Report on Form 10-Q for the quarter ending March 31, 2019.

Revenues (Notes)

Revenues (Notes)	9 Months Ended
	Sep. 30, 2018
Revenue from Contract with Customer [Abstract]
Revenues	3. Revenues Adoption of ASC Topic 606, Revenue from Contracts with Customers (ASC 606) Effective January 1, 2018, the Company adopted ASC 606 using the modified retrospective method, which allows companies to apply the new revenue standard to reporting periods beginning in the year the standard is first implemented, while prior periods continue to be reported in accordance with previous accounting guidance. The adoption of ASC 606 did not have a significant impact on the recognition of revenues; therefore, the Company did not have an opening retained earnings adjustment. Disaggregated revenue disclosures by segment are presented in Note 12. Segment Reporting . Revenue Recognition Revenues are recognized as control of the promised service is transferred to customers, in an amount that reflects the consideration expected in exchange for the services. For the Apex and Oxford segments, revenues from assignment contracts are recognized over time, based on hours worked by the Company’s contract professionals. The performance of the requested service over time is the single performance obligation for assignment revenues. Certain customers may receive discounts (e.g., volume discounts, rebates, prompt-pay discounts) and adjustments to the amounts billed. These discounts, rebates and adjustments are considered variable consideration. Volume discounts are the largest component of variable consideration and are estimated using (i) the most likely amount method prescribed by ASC 606, (ii) contract terms and (iii) estimates of revenue. Revenues are recognized net of variable consideration to the extent it is probable a significant reversal of revenues will not occur in subsequent periods. Permanent placement revenues are recognized at the point in time when employment candidates begin permanent employment. Finding a qualified candidate that the client hires as a permanent employee is a single performance obligation for the Company’s permanent placement contracts. Revenues recognized from permanent placement services are based upon a percentage of the candidates' base salary. The Company records a liability for permanent placement candidates that do not remain with the client through the contingency period, which is typically 90 days or less ("fallouts"). When a fallout occurs, the Company will generally find a replacement candidate at no additional cost to the client. Prior to the adoption of ASC 606, the estimate for permanent placement fallouts was recorded as accounts receivable allowances and effective January 1, 2018 this estimate is considered a contract liability and was $1.5 million . On April 2, 2018, the Company acquired ECS Federal, LLC ("ECS"), which delivers advanced solutions in cloud, cybersecurity, artificial intelligence, machine learning, software development, IT modernization and science and engineering and is primarily focused on federal government activities (see Note 4. Acquisitions ). ECS customer contracts generally contain a single performance obligation involving a significant integration of various activities that are performed together to deliver a combined service or solution. Performance obligations may involve a series of recurring services, such as network operations and maintenance, operation and program support services, IT outsourcing services and other IT arrangements where the Company is standing ready to provide support, when-and-if needed. Performance obligations are satisfied over time because the customer simultaneously receives and consumes the benefits of the Company’s performance as services are provided. ECS provides services under the following types of contracts: Time and materials ("T&M") contracts provide for payments based on fixed hourly rates for each direct labor hour expended and reimbursements for allowable material costs and out-of-pocket expenses. To the extent actual direct labor and associated costs vary in relation to the agreed upon billing rates, the generated profit may vary. Cost-plus-fixed-fee ("CPFF") contracts provide for reimbursement of direct contract costs and allowable and allocable indirect costs, plus a negotiated profit margin or fee. CPFF contracts are usually subject to lower risk and tend to have lower margins. Firm-fixed-price ("FFP") contracts provide for a fixed price for specified services and solutions. If actual costs vary from planned costs on an FFP contract, the Company generates more or less than the planned amount of profit. Revenues for T&M contracts are recognized over time, based on hours worked. Revenues for CPFF contracts, under which the Company bills the customer for actual costs incurred plus a negotiated fee, and FFP contracts are recognized over time, generally based on the amount invoiced as those amounts directly correspond with the value received by a customer. From time to time, the Company may have FFP contracts in which revenues are recognized using a cost-to-cost measurement method. The Company recognizes revenues on a gross basis as it acts as a principal for all of its revenue transactions. The Company has direct contractual relationships with its customers, bears the risks and rewards of its arrangements, has the discretion to select the contract professionals and establish the price for the services to be provided. The Company includes billable expenses (allowable material costs and out-of-pocket reimbursable expenses) in revenues and the associated expenses are included in costs of services. The Company’s contracts have termination for convenience provisions and do not have substantive termination penalties; therefore, the contract duration for accounting purposes may be less than the stated terms. For accounting purposes, the Company's contracts with customers are considered to be of a short-term nature (one year or less). The Company does not disclose the value of remaining performance obligations for short-term contracts. Payment Terms Payment terms vary and the time between invoicing and when payment is due is not significant. There are no financing components to the Company’s arrangements. Contract Liabilities for Advance Payments The Company has contract liabilities for payments received in advance of providing services under certain contracts. Contract liabilities for advance payments were $0.6 million at January 1, 2018 and $6.8 million at September 30, 2018 . The increase in contract liabilities was due to ECS, which had a provisional contract liabilities balance of $11.6 million as of the acquisition date. Acquisition date balances are subject to change during the measurement period (see Note 4. Acquisitions ). Contract liabilities are included in other current liabilities on the condensed consolidated balance sheet. During the three and nine months ended September 30, 2018 , the Company recognized revenues of $8.9 million and $11.5 million , respectively, relating to amounts that were previously included in contract liabilities. Contract Costs There are no incremental costs to obtain contracts. Contract fulfillment costs include, but are not limited to, direct labor for both employees and subcontractors, allowable materials such as third-party hardware and software that are integrated as part of the overall services and solutions provided to customers and out-of-pocket reimbursable expenses. Contract fulfillment costs are expensed as incurred, except for certain set-up costs for an ECS project, which were capitalized and are being amortized over the expected period of benefit. Accounts Receivable Allowances The Company estimates its credit losses (the inability of customers to make required payments) based on (i) a combination of past experience and current trends, (ii) consideration of the current aging of receivables and (iii) a specific review for potential bad debts. The resulting bad debt expense is included in selling, general and administrative ("SG&A") expenses. The accounts receivable allowance was $5.1 million at September 30, 2018 and $9.9 million at December 31, 2017 . The allowance at December 31, 2017 included $3.1 million for estimated permanent placement fallouts and various billing adjustments. Beginning in 2018, with the adoption of ASC 606, the permanent placement fallouts are now included in other current liabilities in the accompanying condensed consolidated balance sheet and billing adjustments are a direct reduction of the gross accounts receivable balance.

Acquisitions (Notes)

Acquisitions (Notes)	9 Months Ended
	Sep. 30, 2018
Business Combinations [Abstract]
Acquisitions [Text Block]	4. Acquisitions On April 2, 2018 , the Company acquired all of the outstanding equity interests of ECS, headquartered in Fairfax, Virginia for $775.0 million , resulting in ECS becoming a wholly-owned subsidiary of the Company. Acquisition expenses were approximately $12.0 million and were expensed as incurred and included in SG&A expenses. ECS delivers advanced solutions in cloud, cybersecurity, artificial intelligence, machine learning, software development, IT modernization and science and engineering and is primarily focused on federal government activities. ECS was purchased to complement and elevate our offerings and strengthen the Company's position as a premier IT and professional services provider by entering the government services space . ECS is reported as a separate segment of the Company. The results of operations of ECS have been included in the consolidated results of the Company from the date of acquisition. The condensed consolidated statements of operations and comprehensive income for the three and nine months ended September 30, 2018 included ECS revenues of $164.0 million and $319.1 million , respectively and operating income of $4.3 million and $8.0 million , respectively. Assets and liabilities of all acquired companies are recorded at their estimated fair values at the dates of acquisition. The fair value assigned to identifiable intangible assets is determined primarily by using a discounted cash flow method (a non-recurring fair value measurement based on Level 3 inputs). Goodwill represents the acquired assembled workforce, potential new customers and future cash flows after the acquisition. Goodwill related to this acquisition totaled $527.4 million , of which $507.6 million is estimated to be deductible for income tax purposes. The purchase accounting for the acquisition of ECS remains incomplete with respect to opening tangible assets, intangible assets, liabilities and taxes, as management continues to gather and evaluate information about circumstances that existed as of the acquisition date. Measurement period adjustments will be recognized prospectively within 12 months from the date of acquisition. The following table summarizes the consider ation paid and the provisional fair value of assets acquired and liabilities assumed (in thousands): Cash $ 12,400 Accounts receivable 97,514 Prepaid expenses and other current assets 8,568 Property and equipment 28,977 Identifiable intangible assets 194,850 Goodwill 527,388 Other non-current assets 1,282 Total assets acquired 870,979 Current liabilities 93,900 Long-term liabilities 4,425 Total liabilities assumed 98,325 Total purchase price (1) $ 772,654 _________ (1) This amount represents the $775.0 million in purchase consideration as set forth in the purchase agreement, plus $12.4 million paid for cash acquired and $1.0 million paid for working capital delivered in excess of target working capital, less $15.7 million indebtedness assumed. The following table summarizes the acquired identifiable intangible assets of ECS (in thousands): Useful life Contractual customer relationships 13 years $ 141,400 Backlog 1 year 26,100 Non-compete agreements 4 to 7 years 10,350 Favorable contracts 5 years 500 Trademarks indefinite 16,500 Total identifiable intangible assets acquired $ 194,850 The weighted-average amortization period for identifiable intangible assets, excluding trademarks, is 10.5 years . The summary below (in thousands, except for per share data) presents pro forma unaudited consolidated results of operations for the three and nine months ended September 30, 2018 and 2017 as if the acquisition of ECS by the Company and the acquisition of a business by ECS in April 2017, both occurred on January 1, 2017. The pro forma unaudited consolidated results give effect to, among other things: (i) amortization of intangible assets, (ii) stock-based compensation expense and the related dilution for restricted stock units granted to ECS employees, (iii) interest expense on acquisition-related debt and (iv) the exclusion of nonrecurring expenses incurred by ECS prior to its acquisition by the Company for ECS’ acquisition-related activities and costs incurred in the sale of ECS to the Company. The pro forma unaudited consolidated results are not necessarily indicative of the operating results that would have occurred if the acquisition had been consummated as of the date indicated, nor are they necessarily indicative of future operating results. Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Revenues $ 906,449 $ 820,185 $ 2,619,170 $ 2,381,872 Income from continuing operations $ 49,216 $ 30,246 $ 122,937 $ 66,357 Net income $ 49,172 $ 30,222 $ 122,704 $ 66,204 Earnings per share: Basic $ 0.94 $ 0.58 $ 2.35 $ 1.26 Diluted $ 0.93 $ 0.57 $ 2.32 $ 1.24 Number of shares and share equivalents used to calculate earnings per share: Basic 52,367 52,500 52,298 52,660 Diluted 53,125 53,223 53,085 53,350

Goodwill and Identifiable Asset

Goodwill and Identifiable Assets (Notes)	9 Months Ended
	Sep. 30, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Identifiable Intangible Assets	5. Goodwill and Identifiable Intangible Assets The changes in the carrying amount of goodwill for the nine months ended September 30, 2018 and the year ended December 31, 2017 were as follows (in thousands): Apex Segment Oxford Segment ECS Segment Total Balance as of December 31, 2016 $ 644,617 $ 228,896 $ — $ 873,513 Stratacuity acquisition 17,467 — — 17,467 Translation adjustment — 3,115 — 3,115 Balance as of December 31, 2017 662,084 232,011 — 894,095 ECS acquisition — — 527,388 527,388 Translation adjustment — (847 ) — (847 ) Balance as of September 30, 2018 $ 662,084 $ 231,164 $ 527,388 $ 1,420,636 Acquired intangible assets consisted of the following (in thousands): September 30, 2018 December 31, 2017 Estimated Useful Life Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount Subject to amortization: Customer and contractual relationships 2 - 13 years $ 343,707 $ 135,739 $ 207,968 $ 202,588 $ 119,272 $ 83,316 Contractor relationships 2 - 5 years 71,121 65,102 6,019 71,121 59,174 11,947 Backlog 1 year 26,100 17,400 8,700 — — — Non-compete agreements 2 - 7 years 22,234 8,950 13,284 11,850 6,600 5,250 In-use software 6 years 18,900 15,178 3,722 18,900 12,816 6,084 Favorable contracts 5 years 1,400 804 596 900 673 227 483,462 243,173 240,289 305,359 198,535 106,824 Not subject to amortization: Trademarks 262,268 — 262,268 245,942 — 245,942 Total $ 745,730 $ 243,173 $ 502,557 $ 551,301 $ 198,535 $ 352,766 Estimated future amortization expense is as follows (in thousands): Remainder of 2018 $ 18,545 2019 51,296 2020 40,287 2021 35,469 2022 24,437 Thereafter 70,255 $ 240,289

Long-Term Debt (Notes)

Long-Term Debt (Notes)	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Long-Term Debt	6. Long-Term Debt Long-term debt consisted of the following (in thousands): September 30, December 31, $200 million revolving credit facility, due March 31, 2023 $ — $ — Term B loan facility, due June 5, 2022 392,000 588,000 Term B loan facility, due April 2, 2025 787,000 — 1,179,000 588,000 Unamortized deferred loan costs (24,846 ) (12,787 ) $ 1,154,154 $ 575,213 On April 2, 2018, in connection with the acquisition of ECS, the Company amended its credit facility mainly to add an $822.0 million tranche to the term B loan facility that matures on April 2, 2025. The amendment also provided for the ability to increase the loan facilities by an amount not to exceed the sum of (i) $300.0 million , (ii) the aggregate principal of voluntary prepayments of the term B loans and permanent reductions of the revolving commitments, and (iii) additional amounts so long as the pro forma consolidated secured leverage ratio is no greater than 3.25 to 1.00. The revolving credit facility was also amended to extend the maturity date to March 31, 2023. The Company incurred $22.5 million of debt issuance and amendment costs, of which $15.3 million are presented in the condensed consolidated balance sheet as a reduction of outstanding debt and are being amortized over the term of the credit facility, $6.2 million were expensed as incurred and were included in interest expense in the nine months ended September 30, 2018 , and the remaining fees were presented in other current assets and other non-current assets and are being amortized over the term of the credit facility. Borrowings under the term B loans bear interest at LIBOR, plus 2.00 percent . Borrowings under the revolving credit facility bear interest at LIBOR plus 1.25 to 2.25 percent , or the bank’s base rate plus 0.25 to 1.25 percent , depending on leverage levels. A commitment fee of 0.20 to 0.35 percent is payable on the undrawn portion of the revolving credit facility. For the term B loan that matures on June 5, 2022, there are no required minimum payments until its maturity date. For the term B loan that matures on April 2, 2025, the Company is required to make minimum quarterly payments of $2.1 million ; however, as a result of principal payments made through September 30, 2018 , the first required minimum quarterly payment of $2.1 million is not due until September 30, 2022 . The Company is also required to make mandatory prepayments on its term loans from excess cash flow and with the proceeds of asset sales, debt issuances and specified other events, subject to specified exceptions. The credit facility includes various restrictive covenants including the maximum ratio of consolidated secured debt to consolidated earnings before interest, taxes, depreciation and amortization ("EBITDA"), which steps down at regular intervals from 4.75 to 1.00 as of September 30, 2018 , to 3.75 to 1.00 as of September 30, 2021 and thereafter. The credit facility also contains certain customary limitations including, among other terms and conditions, the Company's ability to incur additional indebtedness, engage in mergers and acquisitions, and declare dividends. At September 30, 2018 , the Company was in compliance with its debt covenants, its ratio of consolidated secured debt to consolidated EBITDA was 2.89 to 1.00, and it had $195.6 million available borrowing capacity under its revolving credit facility.

Commitments and Contingencies (

Commitments and Contingencies (Notes)	9 Months Ended
	Sep. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	7. Commitments and Contingencies The Company h as entered into various non-cancelable operating leases, primarily related to its facilities and certain office equipment used in the ordinary course of business. The Company leases two properties owned by related parties. Rent expense for these two properties was $0.3 million for the three months ended September 30, 2018 and 2017 , and $1.0 million for the nine months ended September 30, 2018 and 2017 . As a result of the acquisition of ECS (see Note 4. Acquisitions ), the Company assumed various operating lease commitments for which total future payments are approximately $27.6 million as of September 30, 2018 , with the last payment scheduled to be in February 2027. The Company carries retention policies for its workers’ compensation liability exposures. The workers' compensation loss reserves are based upon an actuarial study conducted by a third-party specialist. Changes in estimates and differences between estimates and the actual payments for claims are recognized in the period that the estimates change or the payments are made. The workers' compensation loss reserves were approximately $2.2 million and $2.1 million , at September 30, 2018 and December 31, 2017 , net of anticipated insurance and indemnification recoveries of $14.9 million and $12.7 million , at September 30, 2018 and December 31, 2017 , respectively. We have undrawn stand-by letters of credit outstanding to secure obligations for workers’ compensation claims with various insurance carriers. These stand-by letters of credit were $4.4 million at September 30, 2018 and December 31, 2017 . The Company’s deferred compensation plan liability was $6.5 million at September 30, 2018 , and was included in other long-term liabilities. The Company established a rabbi trust to fund the deferred compensation plan (see Note 8. Fair Value Measurements ). Legal Proceedings The Company is involved in various legal proceedings, claims and litigation arising in the ordinary course of business. The Company does not believe that the disposition of matters that are pending or asserted will have a material effect on its condensed consolidated financial statements.

Fair Value Measurements (Notes)

Fair Value Measurements (Notes)	9 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurements	8. Fair Value Measurements The carrying values of cash and cash equivalents, accounts receivable, accounts payable and accrued payroll and contractor professional pay approximate their fair value based on their short-term nature. Long-term debt recorded in the Company’s condensed consolidated balance sheet at September 30, 2018 was $1.2 billion , excluding the $24.8 million of unamortized deferred loan costs (see Note 6. Long-Term Debt ). The fair value of the term B loans was $1.2 billion as of September 30, 2018 and was determined using Level 1 inputs (quoted prices in active markets for identical assets and liabilities) from the fair value hierarchy. The Company had investments, primarily mutual funds, of $6.4 million at September 30, 2018 , held in a rabbi trust restricted to fund the Company's deferred compensation plan. The fair value of these investments was determined using Level 1 inputs from the fair value hierarchy. These assets are included in other non-current assets. Certain assets and liabilities, such as goodwill and trademarks, are not measured at fair value on an ongoing basis but are subject to fair value adjustments in certain circumstances (e.g., when there is evidence of impairment). For the nine months ended September 30, 2018 and 2017 , no fair value adjustments were required for non-financial assets or liabilities.

Stockholders' Equity (Notes)

Stockholders' Equity (Notes)	9 Months Ended
	Sep. 30, 2018
Stockholders' Equity Attributable to Parent [Abstract]
Stockholders' Equity	9. Stockholders' Equity There were 139,241 and 305,348 shares issued upon the vesting of restricted stock units, exercise of stock options and purchases of stock under the Employee Stock Purchase Plan for the three and nine months ended September 30, 2018 , respectively. The accumulated other comprehensive loss balance at September 30, 2018 and December 31, 2017, and other comprehensive income during the nine months ended September 30, 2018 , consists of foreign currency translation adjustments.

Earnings Per Share (Notes)

Earnings Per Share (Notes)	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
Earnings per share	10. Earnings per Share The following is a reconciliation of the shares used to compute basic and diluted earnings per share (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2018 2017 2018 2017 Weighted average number of common shares outstanding used to compute basic earnings per share 52,362 52,500 52,282 52,660 Dilutive effect of stock-based awards 672 673 708 659 Number of shares used to compute diluted earnings per share 53,034 53,173 52,990 53,319 The number of anti-dilutive share equivalents outstanding during the three and nine months ended September 30, 2018 and 2017 was insignificant.

Income Taxes (Notes)

Income Taxes (Notes)	9 Months Ended
	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Income Taxes	11. Income Taxes For interim reporting periods, the Company’s provision for income taxes is calculated using its annualized estimated effective tax rate for the year. This rate is based on its estimated full-year income and the related income tax expense for each jurisdiction in which the Company operates. Changes in the geographical mix, permanent differences or the estimated level of annual pre-tax income, can affect the effective tax rate. This rate is adjusted for the effects of discrete items occurring in the period. On December 22, 2017, Staff Accounting Bulletin No. 118 (“SAB 118”) was issued to address the application of U.S. GAAP in situations when a registrant does not have the necessary information available, prepared, or analyzed (including computations) in reasonable detail to complete the accounting for certain income tax effects of the Tax Cuts and Jobs Act (the "TCJA"). The guidance also provided for a measurement period of up to one year from the date of enactment to complete the accounting for the U.S. tax law changes. In previous quarters, the Company made provisional estimates of the tax effect of the transitional tax liability on deemed foreign dividends, executive compensation and meals and entertainment. Based on guidelines issued by the IRS during the third quarter of 2018, the Company adjusted its provisional estimates and recorded a tax benefit of $2.9 million . The measurement period under SAB 118 remains open as there is still anticipated guidance clarifying certain aspects of the TCJA and any subsequent adjustments to these provisional amounts would be recorded in the fourth quarter of 2018.

Segment Reporting (Notes)

Segment Reporting (Notes)	9 Months Ended
	Sep. 30, 2018
Segment Reporting [Abstract]
Segment Reporting	12. Segment Reporting ASGN is a leading provider of IT and professional services in the technology, creative/digital, engineering and life sciences fields across commercial and government sectors. ASGN operates through its Apex, Oxford and ECS segments. The Apex Segment provides technical, scientific, digital and creative services and solutions to Fortune 1000 and mid-market clients across the United States and Canada. The businesses in this segment include Apex Systems, Apex Life Sciences and Creative Circle. The Oxford Segment provides "hard to find" technical, digital, engineering and life sciences resources and consulting services in select skill and geographic markets. The businesses in this segment include Oxford, CyberCoders and Life Sciences Europe. The ECS Segment delivers advanced solutions in cloud, cybersecurity, artificial intelligence, machine learning, software development, IT modernization and science and engineering and is primarily focused on federal government activities. ECS was acquired on April 2, 2018 (see Note 4. Acquisitions ). The Company’s management evaluates the performance of each segment primarily based on revenues, gross profit and operating income. The information in the following tables is derived directly from the segments’ internal financial reporting used for corporate management purposes. The following tables present revenues, gross profit, operating income and amortization by reportable segment (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2018 2017 2018 2017 Apex: Revenues $ 589,717 $ 517,492 $ 1,695,728 $ 1,502,462 Gross profit 177,831 155,783 506,146 445,925 Operating income 71,443 59,016 192,610 162,679 Amortization 6,546 7,194 19,638 21,983 Oxford: Revenues $ 152,701 $ 149,556 $ 455,222 $ 444,427 Gross profit 62,712 62,532 187,321 183,471 Operating income 15,156 16,088 39,794 39,525 Amortization 1,040 1,054 3,143 3,028 ECS: Revenues $ 164,031 $ — $ 319,181 $ — Gross profit 29,629 — 58,288 — Operating income 4,314 — 8,012 — Amortization 10,954 — 21,908 — Corporate: Operating loss (1) $ (16,616 ) $ (14,234 ) $ (54,745 ) $ (38,265 ) Consolidated: Revenues $ 906,449 $ 667,048 $ 2,470,131 $ 1,946,889 Gross profit 270,172 218,315 751,755 629,396 Operating income 74,297 60,870 185,671 163,939 Amortization 18,540 8,248 44,689 25,011 _____________ (1) Corporate expenses primarily consist of consolidated stock-based compensation expense, compensation for corporate employees, acquisition, integration and strategic planning expenses, public company expenses and depreciation expense for corporate assets. The following table presents our revenues disaggregated by type (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2018 2017 2018 2017 Apex: Assignment $ 575,309 $ 506,376 $ 1,653,835 $ 1,468,976 Permanent placement 14,408 11,116 41,893 33,486 $ 589,717 $ 517,492 $ 1,695,728 $ 1,502,462 Oxford: Assignment $ 130,365 $ 127,963 $ 386,068 $ 379,892 Permanent placement 22,336 21,593 69,154 64,535 $ 152,701 $ 149,556 $ 455,222 $ 444,427 ECS: Firm-fixed-price $ 48,272 $ — $ 93,034 $ — Time and materials 42,102 — 91,097 — Cost-plus-fixed-fee 73,657 — 135,050 — $ 164,031 $ — $ 319,181 $ — Consolidated $ 906,449 $ 667,048 $ 2,470,131 $ 1,946,889 The Company operates internationally, with operations mainly in the United States. The following table presents revenues by geographic location (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2018 % 2017 % 2018 % 2017 % Revenues: Domestic $ 867,754 95.7 % $ 632,584 94.8 % $ 2,352,993 95.3 % $ 1,849,567 95.0 % Foreign 38,695 4.3 % 34,464 5.2 % 117,138 4.7 % 97,322 5.0 % $ 906,449 100.0 % $ 667,048 100.0 % $ 2,470,131 100.0 % $ 1,946,889 100.0 %

Acquisitions (Tables)

Acquisitions (Tables)	9 Months Ended
	Sep. 30, 2018
Business Combinations [Abstract]
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed	The following table summarizes the consider ation paid and the provisional fair value of assets acquired and liabilities assumed (in thousands): Cash $ 12,400 Accounts receivable 97,514 Prepaid expenses and other current assets 8,568 Property and equipment 28,977 Identifiable intangible assets 194,850 Goodwill 527,388 Other non-current assets 1,282 Total assets acquired 870,979 Current liabilities 93,900 Long-term liabilities 4,425 Total liabilities assumed 98,325 Total purchase price (1) $ 772,654 _________ (1) This amount represents the $775.0 million in purchase consideration as set forth in the purchase agreement, plus $12.4 million paid for cash acquired and $1.0 million paid for working capital delivered in excess of target working capital, less $15.7 million indebtedness assumed.
Finite-Lived and Indefinite-Lived Intangible Assets Acquired as Part of Business Combination	The following table summarizes the acquired identifiable intangible assets of ECS (in thousands): Useful life Contractual customer relationships 13 years $ 141,400 Backlog 1 year 26,100 Non-compete agreements 4 to 7 years 10,350 Favorable contracts 5 years 500 Trademarks indefinite 16,500 Total identifiable intangible assets acquired $ 194,850 The weighted-average amortization period for identifiable intangible assets, excluding trademarks, is 10.5 years .
Business Acquisition, Pro Forma Information	The summary below (in thousands, except for per share data) presents pro forma unaudited consolidated results of operations for the three and nine months ended September 30, 2018 and 2017 as if the acquisition of ECS by the Company and the acquisition of a business by ECS in April 2017, both occurred on January 1, 2017. The pro forma unaudited consolidated results give effect to, among other things: (i) amortization of intangible assets, (ii) stock-based compensation expense and the related dilution for restricted stock units granted to ECS employees, (iii) interest expense on acquisition-related debt and (iv) the exclusion of nonrecurring expenses incurred by ECS prior to its acquisition by the Company for ECS’ acquisition-related activities and costs incurred in the sale of ECS to the Company. The pro forma unaudited consolidated results are not necessarily indicative of the operating results that would have occurred if the acquisition had been consummated as of the date indicated, nor are they necessarily indicative of future operating results. Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Revenues $ 906,449 $ 820,185 $ 2,619,170 $ 2,381,872 Income from continuing operations $ 49,216 $ 30,246 $ 122,937 $ 66,357 Net income $ 49,172 $ 30,222 $ 122,704 $ 66,204 Earnings per share: Basic $ 0.94 $ 0.58 $ 2.35 $ 1.26 Diluted $ 0.93 $ 0.57 $ 2.32 $ 1.24 Number of shares and share equivalents used to calculate earnings per share: Basic 52,367 52,500 52,298 52,660 Diluted 53,125 53,223 53,085 53,350

Goodwill and Identifiable Ass_2

Goodwill and Identifiable Assets (Tables)	9 Months Ended
	Sep. 30, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill	The changes in the carrying amount of goodwill for the nine months ended September 30, 2018 and the year ended December 31, 2017 were as follows (in thousands): Apex Segment Oxford Segment ECS Segment Total Balance as of December 31, 2016 $ 644,617 $ 228,896 $ — $ 873,513 Stratacuity acquisition 17,467 — — 17,467 Translation adjustment — 3,115 — 3,115 Balance as of December 31, 2017 662,084 232,011 — 894,095 ECS acquisition — — 527,388 527,388 Translation adjustment — (847 ) — (847 ) Balance as of September 30, 2018 $ 662,084 $ 231,164 $ 527,388 $ 1,420,636
Schedule of Acquired Intangible Assets	Acquired intangible assets consisted of the following (in thousands): September 30, 2018 December 31, 2017 Estimated Useful Life Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount Subject to amortization: Customer and contractual relationships 2 - 13 years $ 343,707 $ 135,739 $ 207,968 $ 202,588 $ 119,272 $ 83,316 Contractor relationships 2 - 5 years 71,121 65,102 6,019 71,121 59,174 11,947 Backlog 1 year 26,100 17,400 8,700 — — — Non-compete agreements 2 - 7 years 22,234 8,950 13,284 11,850 6,600 5,250 In-use software 6 years 18,900 15,178 3,722 18,900 12,816 6,084 Favorable contracts 5 years 1,400 804 596 900 673 227 483,462 243,173 240,289 305,359 198,535 106,824 Not subject to amortization: Trademarks 262,268 — 262,268 245,942 — 245,942 Total $ 745,730 $ 243,173 $ 502,557 $ 551,301 $ 198,535 $ 352,766
Schedule of Estimated Future Amortization Expense	Estimated future amortization expense is as follows (in thousands): Remainder of 2018 $ 18,545 2019 51,296 2020 40,287 2021 35,469 2022 24,437 Thereafter 70,255 $ 240,289

Long-Term Debt (Tables)

Long-Term Debt (Tables)	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Schedule of Long-term Debt	Long-term debt consisted of the following (in thousands): September 30, December 31, $200 million revolving credit facility, due March 31, 2023 $ — $ — Term B loan facility, due June 5, 2022 392,000 588,000 Term B loan facility, due April 2, 2025 787,000 — 1,179,000 588,000 Unamortized deferred loan costs (24,846 ) (12,787 ) $ 1,154,154 $ 575,213

Earnings Per Share (Tables)

Earnings Per Share (Tables)	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
Reconciliation of Shares Used to Compute Basic and Diluted Earnings per Share	The following is a reconciliation of the shares used to compute basic and diluted earnings per share (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2018 2017 2018 2017 Weighted average number of common shares outstanding used to compute basic earnings per share 52,362 52,500 52,282 52,660 Dilutive effect of stock-based awards 672 673 708 659 Number of shares used to compute diluted earnings per share 53,034 53,173 52,990 53,319

Segment Reporting (Tables)

Segment Reporting (Tables)	9 Months Ended
	Sep. 30, 2018
Segment Reporting Information [Line Items]
Schedule of Segment Reporting Information, by Segment	The following tables present revenues, gross profit, operating income and amortization by reportable segment (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2018 2017 2018 2017 Apex: Revenues $ 589,717 $ 517,492 $ 1,695,728 $ 1,502,462 Gross profit 177,831 155,783 506,146 445,925 Operating income 71,443 59,016 192,610 162,679 Amortization 6,546 7,194 19,638 21,983 Oxford: Revenues $ 152,701 $ 149,556 $ 455,222 $ 444,427 Gross profit 62,712 62,532 187,321 183,471 Operating income 15,156 16,088 39,794 39,525 Amortization 1,040 1,054 3,143 3,028 ECS: Revenues $ 164,031 $ — $ 319,181 $ — Gross profit 29,629 — 58,288 — Operating income 4,314 — 8,012 — Amortization 10,954 — 21,908 — Corporate: Operating loss (1) $ (16,616 ) $ (14,234 ) $ (54,745 ) $ (38,265 ) Consolidated: Revenues $ 906,449 $ 667,048 $ 2,470,131 $ 1,946,889 Gross profit 270,172 218,315 751,755 629,396 Operating income 74,297 60,870 185,671 163,939 Amortization 18,540 8,248 44,689 25,011 _____________ (1) Corporate expenses primarily consist of consolidated stock-based compensation expense, compensation for corporate employees, acquisition, integration and strategic planning expenses, public company expenses and depreciation expense for corporate assets.
Disaggregation of Revenue [Table Text Block]	The following table presents our revenues disaggregated by type (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2018 2017 2018 2017 Apex: Assignment $ 575,309 $ 506,376 $ 1,653,835 $ 1,468,976 Permanent placement 14,408 11,116 41,893 33,486 $ 589,717 $ 517,492 $ 1,695,728 $ 1,502,462 Oxford: Assignment $ 130,365 $ 127,963 $ 386,068 $ 379,892 Permanent placement 22,336 21,593 69,154 64,535 $ 152,701 $ 149,556 $ 455,222 $ 444,427 ECS: Firm-fixed-price $ 48,272 $ — $ 93,034 $ — Time and materials 42,102 — 91,097 — Cost-plus-fixed-fee 73,657 — 135,050 — $ 164,031 $ — $ 319,181 $ — Consolidated $ 906,449 $ 667,048 $ 2,470,131 $ 1,946,889
Schedule of Revenue by Geographical Areas	The Company operates internationally, with operations mainly in the United States. The following table presents revenues by geographic location (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2018 % 2017 % 2018 % 2017 % Revenues: Domestic $ 867,754 95.7 % $ 632,584 94.8 % $ 2,352,993 95.3 % $ 1,849,567 95.0 % Foreign 38,695 4.3 % 34,464 5.2 % 117,138 4.7 % 97,322 5.0 % $ 906,449 100.0 % $ 667,048 100.0 % $ 2,470,131 100.0 % $ 1,946,889 100.0 %

Revenues (Details)

Revenues (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2017
Revenue from Contract with Customer [Abstract]
Contract with Customer, Refund Liability			$ 1,500
Deferred Revenue	$ 6,830	$ 6,830	560
Contract with Customer, Liability, Increase (Decrease) for Contract Acquired in Business Combination		11,580
Contract with Customer, Liability, Revenue Recognized	8,900	11,500
Allowance for Doubtful Accounts Receivable, Current	$ 5,120	$ 5,120	9,910
permanent placement fallouts and other revenue adjustments			$ 3,100

Acquisitions (Details)

Acquisitions (Details) - USD ($) $ in Thousands	Apr. 02, 2018	Sep. 30, 2018
Acquired Finite-Lived Intangible Assets [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets	$ 194,850
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life		10 years 6 months
Customer Contractual Relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	13 years
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill	$ 141,400
Backlog [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	1 year
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill	$ 26,100
Noncompete Agreements [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill	$ 10,350
Favorable Contracts [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	5 years
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill	$ 500
Trademarks [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill	$ 16,500
Minimum [Member] | Customer Contractual Relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life		2 years
Minimum [Member] | Backlog [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life		1 year
Minimum [Member] | Noncompete Agreements [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	4 years	2 years
Minimum [Member] | Favorable Contracts [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life		5 years
Maximum [Member] | Customer Contractual Relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life		13 years
Maximum [Member] | Noncompete Agreements [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	7 years	7 years

Acquisitions Business Combinati

Acquisitions Business Combinations Additional Information (Details) - USD ($) $ in Thousands	Apr. 02, 2018	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2017
Business Combinations [Abstract]
Business Acquisition, Effective Date of Acquisition	Apr. 2, 2018
Business Acquisition, Name of Acquired Entity	ECS, headquartered in Fairfax, Virginia
Payments to Acquire Businesses, Gross			$ 775,000
Business Acquisition, Transaction Costs		$ 12,040	12,040
Business Combination, Reason for Business Combination	was purchased to complement and elevate our offerings and strengthen the Company's position as a premier IT and professional services provider by entering the government services space
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual		164,000	319,100
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual		4,310	8,010
Goodwill	$ 527,388	1,420,636	1,420,636	$ 894,095
Business Acquisition, Goodwill, Expected Tax Deductible Amount		$ 507,600	$ 507,600

Acquisitions Business Combina_2

Acquisitions Business Combinations Purchase Accounting Assets Liabilities (Details) - USD ($) $ in Thousands		9 Months Ended
		Sep. 30, 2018	Apr. 02, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents			$ 12,400
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables			97,514
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Prepaid Expense and Other Assets			8,568
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment			28,977
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets			194,850
Goodwill		$ 1,420,636	527,388	$ 894,095
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets			1,282
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets			870,979
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities			93,900
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities			4,425
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities			98,325
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net	[1]		$ 772,654
Goodwill, Purchase Accounting Adjustments		1,000
Liabilities Assumed		$ 15,700
[1]	This amount represents the $775.0 million in purchase consideration as set forth in the purchase agreement, plus $12.4 million paid for cash acquired and $1.0 million paid for working capital delivered in excess of target working capital, less $15.7 million indebtedness assumed

Acquisitions Pro Forma (Details

Acquisitions Pro Forma (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Business Combinations Pro Forma [Abstract]
Business Acquisition, Pro Forma Revenue	$ 906,449	$ 820,185	$ 2,619,170	$ 2,381,872
Business Acquisition, Pro Forma Income (Loss) from Continuing Operations, Net of Tax	49,216	30,246	122,937	66,357
Business Acquisition, Pro Forma Net Income (Loss)	$ 49,172	$ 30,222	$ 122,704	$ 66,204
Business Acquisition, Pro Forma Income (Loss) from Continuing Operations, Net of Tax, Per Share, Basic	$ 0.94	$ 0.58	$ 2.35	$ 1.26
Business Acquisition, Pro Forma Income (Loss) from Continuing Operations, Net of Tax, Per Share, Diluted	$ 0.93	$ 0.57	$ 2.32	$ 1.24
Weighted Average Basic Shares Outstanding, Pro Forma	52,367	52,500	52,298	52,660
Pro Forma Weighted Average Shares Outstanding, Diluted	53,125	53,223	53,085	53,350

Goodwill and Identifiable Ass_3

Goodwill and Identifiable Assets (Goodwill) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Apr. 02, 2018	Dec. 31, 2016
Goodwill [Roll Forward]
Gross goodwill	$ 1,420,636	$ 894,095		$ 873,513
Goodwill, Acquired During Period	527,388	17,467
Goodwill	1,420,636	894,095	$ 527,388
Translation adjustment	(847)	3,115
Apex
Goodwill [Roll Forward]
Gross goodwill	662,084	662,084		644,617
Translation adjustment		0
Oxford
Goodwill [Roll Forward]
Gross goodwill	231,164	232,011		$ 228,896
Translation adjustment	(847)	3,115
ECS
Goodwill [Roll Forward]
Gross goodwill	527,388
Stratacuity [Member] | Apex
Goodwill [Roll Forward]
Goodwill, Acquired During Period		$ 17,467
ECS | ECS
Goodwill [Roll Forward]
Goodwill, Acquired During Period	$ 527,388

Goodwill and Identifiable Ass_4

Goodwill and Identifiable Assets (Acquired Intangible Assets) (Details) - USD ($) $ in Thousands	Apr. 02, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Intangible Assets [Line Items]
Amortization of intangible assets		$ 18,540	$ 8,248	$ 44,689	$ 25,011
Intangible assets subject to amortization:
Gross Carrying Amount		483,462		483,462		$ 305,359
Accumulated Amortization		243,173		243,173		198,535
Net Carrying Amount		240,289		240,289		106,824
Intangible assets not subject to amortization:
Trademarks, Carrying Amount		262,268		262,268		245,942
Goodwill, Carrying Amount	$ 527,388	1,420,636		1,420,636		894,095
Intangible Assets, Gross (Excluding Goodwill)		745,730		745,730		551,301
Total
Intangible Assets, Net (Excluding Goodwill)		502,557		502,557		352,766
Customer Contractual Relationships
Intangible Assets [Line Items]
Estimated Useful Life	13 years
Intangible assets subject to amortization:
Gross Carrying Amount		343,707		343,707		202,588
Accumulated Amortization		135,739		135,739		119,272
Net Carrying Amount		207,968		$ 207,968		83,316
Customer Contractual Relationships | Minimum [Member]
Intangible Assets [Line Items]
Estimated Useful Life				2 years
Customer Contractual Relationships | Maximum [Member]
Intangible Assets [Line Items]
Estimated Useful Life				13 years
Contractor Relations [Member]
Intangible assets subject to amortization:
Gross Carrying Amount		71,121		$ 71,121		71,121
Accumulated Amortization		65,102		65,102		59,174
Net Carrying Amount		6,019		$ 6,019		11,947
Contractor Relations [Member] | Minimum [Member]
Intangible Assets [Line Items]
Estimated Useful Life				2 years
Contractor Relations [Member] | Maximum [Member]
Intangible Assets [Line Items]
Estimated Useful Life				5 years
Backlog [Member]
Intangible Assets [Line Items]
Estimated Useful Life	1 year
Intangible assets subject to amortization:
Gross Carrying Amount		26,100		$ 26,100		0
Accumulated Amortization		17,400		17,400		0
Net Carrying Amount		8,700		$ 8,700		0
Backlog [Member] | Minimum [Member]
Intangible Assets [Line Items]
Estimated Useful Life				1 year
Non-compete agreements
Intangible assets subject to amortization:
Gross Carrying Amount		22,234		$ 22,234		11,850
Accumulated Amortization		8,950		8,950		6,600
Net Carrying Amount		13,284		$ 13,284		5,250
Non-compete agreements | Minimum [Member]
Intangible Assets [Line Items]
Estimated Useful Life	4 years			2 years
Non-compete agreements | Maximum [Member]
Intangible Assets [Line Items]
Estimated Useful Life	7 years			7 years
Favorable Contracts [Member]
Intangible Assets [Line Items]
Estimated Useful Life	5 years
Intangible assets subject to amortization:
Gross Carrying Amount		1,400		$ 1,400		900
Accumulated Amortization		804		804		673
Net Carrying Amount		596		$ 596		227
Favorable Contracts [Member] | Minimum [Member]
Intangible Assets [Line Items]
Estimated Useful Life				5 years
Computer Software, Intangible Asset [Member]
Intangible assets subject to amortization:
Gross Carrying Amount		18,900		$ 18,900		18,900
Accumulated Amortization		15,178		15,178		12,816
Net Carrying Amount		$ 3,722		$ 3,722		$ 6,084
Computer Software, Intangible Asset [Member] | Minimum [Member]
Intangible Assets [Line Items]
Estimated Useful Life				6 years

Goodwill and Identifiable Ass_5

Goodwill and Identifiable Assets (Future Amortization Expense) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization of intangible assets	$ 18,540	$ 8,248	$ 44,689	$ 25,011
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
2,018	18,545		18,545
2,019	51,296		51,296
2,020	40,287		40,287
2,021	35,469		35,469
2,022	24,437		24,437
Thereafter	70,255		70,255
Net Carrying Amount	$ 240,289		$ 240,289		$ 106,824

Long-Term Debt Schedule (Detail

Long-Term Debt Schedule (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Secured Debt	$ 1,179,000	$ 588,000
Unamortized deferred loan costs	(24,846)	(12,787)
Long-term Debt	1,154,154	575,213
$200 Million Revolving Credit Facility, Due March 2023 [Member]
Debt Instrument [Line Items]
Secured Debt	0	0
$825 Million Term B Loan Facility, due June 2022 [Member]
Debt Instrument [Line Items]
Secured Debt	392,000	588,000
$822 Million Term B Loan Facility, due April 2025 [Member]
Debt Instrument [Line Items]
Secured Debt	$ 787,000	$ 0

Long-term Debt (Details)

Long-term Debt (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2018USD ($)Rate	Dec. 31, 2017USD ($)
Debt Instrument [Line Items]
Unamortized deferred loan costs | $	$ 24,846	$ 12,787
Long-term Debt | $	1,154,154	$ 575,213
Line of Credit Facility, Maximum Borrowing Capacity | $	$ 300,000
Pro Forma Consolidated Leverage Ratio	3.25%
FeesPaidInConnectionWithAmendment | $	$ 22,450
Unamortized Loan Commitment and Origination Fees and Unamortized Discounts or Premiums | $	15,300
Interest Expense, Debt | $	6,160
Contractual Quarterly Payments | $	$ 2,100
Leverage Ratio	2.89
$822 Million Term B Loan Facility, due April 2025 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount | $	$ 822,000
Maximum [Member]
Debt Instrument [Line Items]
Leverage Ratio	4.75%
Leverage Ratio in Latest Year of Debt Term	3.75%
Notes Payable to Banks [Member] | Minimum [Member] | $200 Million Revolving Credit Facility, Due March 2023 [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	0.25%
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.20%
Notes Payable to Banks [Member] | Minimum [Member] | Eurodollar [Member] | $200 Million Revolving Credit Facility, Due March 2023 [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	1.25%
Notes Payable to Banks [Member] | Maximum [Member] | $200 Million Revolving Credit Facility, Due March 2023 [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	1.25%
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.35%
Notes Payable to Banks [Member] | Maximum [Member] | Eurodollar [Member] | $200 Million Revolving Credit Facility, Due March 2023 [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	2.25%
Notes Payable to Banks [Member] | Maximum [Member] | Eurodollar [Member] | $825 Million Term B Loan Facility, due June 2022 [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	2.00%
$200 Million Revolving Credit Facility, Due March 2023 [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Remaining Borrowing Capacity | $	$ 195,600

Commitments and Contingencies_2

Commitments and Contingencies (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018USD ($)property	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)property	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)
Other Commitments [Line Items]
Number of Leased Properties Owned by Related Parties | property	2		2
Costs and Expenses, Related Party	$ 320	$ 320	$ 950	$ 950
Operating Leases, Future Minimum Payments Due	27,600		27,600
Self Insurance Reserve	2,250		2,250		$ 2,080
Estimated Insurance Recoveries	14,890		14,890		12,702
Letters of Credit Outstanding, Amount	4,390		4,390		$ 4,410
Deferred Compensation Liability, Noncurrent	$ 6,480		$ 6,480

Fair Value Measurements (Fair V

Fair Value Measurements (Fair Value Inputs, Liabilities, Quantitative Information) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Fair Value Inputs, Liabilities, Quantitative Information
Secured Debt	$ 1,179,000	$ 588,000
Unamortized deferred loan costs	24,846	$ 12,787
Level 1 Inputs
Fair Value Inputs, Liabilities, Quantitative Information
Long-term debt, fair value	1,184,600
Deferred Compensation Plan Assets	$ 6,440

Stockholders' Equity Shares iss

Stockholders' Equity Shares issued for RSU's, Options and ESPP (Details) - shares	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018
Shares Issued for RSU's, Options and ESPP [Abstract]
Stock Issued During Period, Shares, New Issues	139,241	305,348

Earnings Per Share (Details)

Earnings Per Share (Details) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Weighted Average Number of Shares Outstanding Reconciliation
Weighted average number of common shares outstanding used to compute basic earnings per share	52,362	52,500	52,282	52,660
Dilutive effect of stock-based awards	672	673	708	659
Number of shares used to compute diluted earnings per share	53,034	53,173	52,990	53,319

Income Taxes (Details)

Income Taxes (Details) $ in Millions	9 Months Ended
	Sep. 30, 2018USD ($)
Income Tax Disclosure [Abstract]
Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions	$ 2.9

Segment Reporting (Segment Repo

Segment Reporting (Segment Reporting Information) (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual		$ 4,310		$ 8,010
Revenues:
Revenues		906,449	$ 667,048	2,470,131	$ 1,946,889
Gross Profit:
Total Gross Profit		270,172	218,315	751,755	629,396
Operating Income (Loss):
Total Operating Income		74,297	60,870	185,671	163,939
Amortization of Intangible Assets		18,540	8,248	44,689	25,011
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual		164,000		319,100
Apex
Revenues:
Revenues		589,717	517,492	1,695,728	1,502,462
Gross Profit:
Total Gross Profit		177,831	155,783	506,146	445,925
Operating Income (Loss):
Total Operating Income		71,443	59,016	192,610	162,679
Amortization of Intangible Assets		6,546	7,194	19,638	21,983
Oxford
Revenues:
Revenues		152,701	149,556	455,222	444,427
Gross Profit:
Total Gross Profit		62,712	62,532	187,321	183,471
Operating Income (Loss):
Total Operating Income		15,156	16,088	39,794	39,525
Amortization of Intangible Assets		1,040	1,054	3,143	3,028
ECS
Revenues:
Revenues		164,031	0	319,181	0
Gross Profit:
Total Gross Profit		29,629	0	58,288	0
Operating Income (Loss):
Total Operating Income			0	8,012	0
Amortization of Intangible Assets		10,954	0	21,908	0
Corporate
Operating Income (Loss):
Total Operating Income	[1]	(16,616)	(14,234)	(54,745)	(38,265)
Assignment | Apex
Revenues:
Revenues		575,309	506,376	1,653,835	1,468,976
Assignment | Oxford
Revenues:
Revenues		130,365	127,963	386,068	379,892
Permanent placement | Apex
Revenues:
Revenues		14,408	11,116	41,893	33,486
Permanent placement | Oxford
Revenues:
Revenues		22,336	21,593	69,154	64,535
Fixed-price Contract | ECS
Revenues:
Revenues		48,272	0	93,034	0
Time-and-materials Contract | ECS
Revenues:
Revenues		42,102	0	91,097	0
Cost-plus-fixed-fee Contract | ECS
Revenues:
Revenues		$ 73,657	$ 0	$ 135,050	$ 0
[1]	Corporate expenses primarily consist of consolidated stock-based compensation expense, compensation for corporate employees, acquisition, integration and strategic planning expenses, public company expenses and depreciation expense for corporate assets.

Segment Reporting (Revenue by G

Segment Reporting (Revenue by Geographical Areas) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenues from External Customers [Line Items]
Revenues	$ 906,449	$ 667,048	$ 2,470,131	$ 1,946,889
Revenue as Percentage of Consolidated Revenue	100.00%	100.00%	100.00%	100.00%
Domestic [Member]
Revenues from External Customers [Line Items]
Revenues	$ 867,754	$ 632,584	$ 2,352,993	$ 1,849,567
Revenue as Percentage of Consolidated Revenue	95.70%	94.80%	95.30%	95.00%
Foreign [Member]
Revenues from External Customers [Line Items]
Revenues	$ 38,695	$ 34,464	$ 117,138	$ 97,322
Revenue as Percentage of Consolidated Revenue	4.30%	5.20%	4.70%	5.00%