Acquisitions Acquisitions Costs, by Acquisition (Details) - USD ($) $ in Thousands			6 Months Ended	12 Months Ended
	Jun. 05, 2015	Apr. 14, 2015	Jun. 30, 2015	Dec. 31, 2015
Business Acquisition [Line Items]
BusinessCombinationRecognizedGoodwill	$ 358,000
Creative Circle [Member]
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition	Jun. 05, 2015
Business Acquisition, Name of Acquired Entity	Creative Circle, LLC
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
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned	30,200
Stock Issued During Period, Shares, Acquisitions			794,700
Business Acquisition Contingent Consideration At Fair Value Accrued Earn-Out	13,800
BusinessCombinationRecognizedGoodwill	358,029
Business Combination, Acquisition Related Costs				$ 5,700
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill	194,500
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
BusinessCombinationRecognizedGoodwill		6,449
Business Combination, Acquisition Related Costs				$ 400
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill		7,528
Contractor Relations [Member] | Creative Circle [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill	29,500
Contractor Relations [Member] | LabResource [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill		947
Customer relations | Creative Circle [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill	90,700
Customer relations | LabResource [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill		5,421
Non-compete agreements | Creative Circle [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill	7,300
Non-compete agreements | LabResource [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill		20
Contract-Based Intangible Assets [Member] | Creative Circle [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill	$ 900
Contract-Based Intangible Assets [Member] | LabResource [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill		$ 0