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Stock-Based Compensation (Details 4) - Performance-based restricted stock units [Member] - TSR [Member]
9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Assumptions used to estimate fair value of TSR PBRSUs    
Expected volatility - Medidata 42.00% 48.00%
Expected volatility - Comparison index 43.00% 43.00%
Expected term 2 years 10 months 5 days 2 years 10 months 4 days
Risk-free interest rate 1.40% 0.91%
Dividend yield 0.00% 0.00%