Business Segments (Tables)

12 Months Ended

Dec. 31, 2020

Revenue from External Customer [Line Items]

Schedule of Segment Reporting Information, by Segment [Table Text Block]

	Year Ended December 31,
	2020		2019		2018
Apex
Revenues	$	2,421.2	$	2,520.0	$	2,300.3
Gross profit	710.8		746.0		687.9
Operating income	276.6		287.7		262.4
Amortization	22.9		20.3		26.2
Oxford
Revenues	$	525.2	$	605.7	$	606.5
Gross profit	209.6		242.9		248.9
Operating income	43.9		48.4		54.1
Amortization	0.7		3.7		4.2
ECS
Revenues	$	1,004.2	$	798.2	$	493.0
Gross profit	168.9		141.1		86.9
Operating income	58.0		42.2		15.5
Amortization	28.1		27.1		28.1
Consolidated
Revenues	$	3,950.6	$	3,923.9	$	3,399.8
Gross profit	1,089.3		1,130.0		1,023.7
Operating income(1)	310.4		308.6		260.2
Amortization	51.7		51.1		58.5

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(1) Consolidated operating income includes corporate operating expenses that are not allocated to the segments, consisting 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.

Revenue from External Customers by Geographic Areas [Table Text Block]

The Company operates internationally, with operations in Europe, Canada and Mexico. Most of the Company's revenues are generated in the United States. Revenues from outside the United States accounted for less than 5.0 percent of consolidated revenues for 2020, 2019 and 2018. The following table presents revenues by geographic location (in millions):

	Year Ended December 31,
	2020		2019		2018
Domestic	$	3,778.1	$	3,749.2	$	3,241.8
Foreign	172.5		174.7		158.0
	$	3,950.6	$	3,923.9	$	3,399.8

Long-lived Assets by Geographic Areas [Table Text Block]

The following table presents long-lived assets by geographic location (in millions):

	December 31,
	2020		2019
Domestic	$	67.6	$	71.4
Foreign	1.8		2.3
	$	69.4	$	73.7

Disaggregation of Revenue [Table Text Block]

The following table presents disaggregated revenues by type (in millions):

	Year Ended December 31,
	2020		2019		2018
Apex
Assignment	$	2,040.3	$	2,190.9	$	2,050.1
Consulting	380.9		329.1		250.2
	2,421.2		2,520.0		2,300.3
Oxford
Assignment	468.6		549.4		558.1
Consulting	56.6		56.3		48.4
	525.2		605.7		606.5
ECS
Firm-fixed-price	272.0		214.0		133.1
Time and materials	322.6		267.8		143.4
Cost reimbursable	409.6		316.4		216.5
	1,004.2		798.2		493.0
Consolidated	$	3,950.6	$	3,923.9	$	3,399.8

ECS

Revenue from External Customer [Line Items]

Revenue from External Customers by Products and Services [Table Text Block]

The following table presents the ECS segment revenues by customer type (in millions):

	Year Ended December 31,
	2020		2019		2018
Department of Defense and Intelligence Agencies	$	558.5	$	453.9	$	311.0
Federal Civilian	370.6		293.6		150.9
Other	75.1		50.7		31.1
	$	1,004.2	$	798.2	$	493.0