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.

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.