Stock-based compensation	3 Months Ended
Stock-based compensation	Mar. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Incentive Award Plan and Employee Stock Purchase Plan	10. Stock-based compensation On March 31, 2015, the Company issued 125,101 shares of common stock under the On Assignment 2010 Employee Stock Purchase Plan (the "ESPP"). Compensation expense related to stock-based compensation, including the ESPP, was $4.0 million and $3.1 million for the three months ended March 31, 2015 and 2014, respectively. Stock-based compensation is included in the condensed consolidated statements of operations and comprehensive income in selling, general and administrative expenses.

The entire disclosure for compensation-related costs for equity-based compensation, which may include disclosure of policies, compensation plan details, allocation of equity compensation, incentive distributions, equity-based arrangements to obtain goods and services, deferred compensation arrangements, employee stock ownership plan details and employee stock purchase plan details.

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