Acquisitions Acquisitions (Acquisition Costs, by Acquisition) (Details) - USD ($)			1 Months Ended	6 Months Ended	12 Months Ended
	Jun. 05, 2015	Apr. 14, 2015	Dec. 31, 2013	Jun. 30, 2015	Dec. 31, 2015	Dec. 31, 2013	Dec. 05, 2013
Business Acquisition [Line Items]
Stock Issued During Period, Value, Acquisitions					$ 30,183,000
Stock Issued During Period, Shares, Acquisitions					794,700
Creative Circle [Member]
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition	Jun. 05, 2015
Business Acquisition, Name of Acquired Entity	Creative Circle.
Business Acquisition, Description of Acquired Entity	is headquartered in Los Angeles, California
Business Combination, Reason for Business Combination	was purchased to expand the Company’s technical and creative staffing services
Payments to Acquire Businesses, Gross	$ 540,000,000
Stock Issued During Period, Value, Acquisitions				$ 30,200,000
Stock Issued During Period, Shares, Acquisitions				794,700,000
Business Acquisition, Goodwill, Expected Tax Deductible Amount	358,029,000
Business Acquisition Contingent Consideration At Fair Value Accrued Earn-Out	$ 13,800,000
Business Combination, Acquisition Related Costs					$ 5,700,000
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual					167,200,000
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual					22,900,000
LabResource [Member]
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition		Apr. 14, 2015
Business Acquisition, Name of Acquired Entity		LabResource B.V.
Business Acquisition, Description of Acquired Entity		headquartered in Amsterdam, Netherlands
Business Combination, Reason for Business Combination		expand the Company's life sciences staffing business in Europe
Payments to Acquire Businesses, Gross		$ 12,700,000
Business Combination, Acquisition Related Costs					400,000
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual					7,700,000
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual					$ 1,000,000
CyberCoders [Member]
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition			Dec. 05, 2013
Business Acquisition, Name of Acquired Entity			CyberCoders
Business Acquisition, Description of Acquired Entity			a provider of permanent placement services headquartered in Irvine, California.
Business Combination, Reason for Business Combination			The primary reason for the acquisition was to expand the Company's permanent placement services.
Payments to Acquire Businesses, Gross			$ 93,600,000
Business Combination, Consideration Transferred			96,600,000
Business Acquisition, Goodwill, Expected Tax Deductible Amount							$ 10,300,000
Business Acquisition Contingent Consideration At Fair Value Accrued Earn-Out			$ 3,000,000
contingent consideration maximum							$ 11,000,000
Business Combination, Acquisition Related Costs						$ 1,500,000