Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2015

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Components of stock-based compensation expense

For the three and six months endedJune 30, 2015 and 2014, the components of stock-based compensation expense were as follows (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2015		2014		2015		2014
Stock options	$	1,689	$	1,245	$	2,836	$	2,459
Restricted stock awards and units	5,082		3,307		9,303		6,476
Performance-based restricted stock units	6,377		3,700		11,582		8,450
Employee stock purchase plan	988		378		2,085		944
Total stock-based compensation	$	14,136	$	8,630	$	25,806	$	18,329

Fair value of stock option grants

The fair value of each stock option granted during the three and six months endedJune 30, 2015 and 2014 was estimated on the date of grant using the Black-Scholes pricing model with the following weighted-average assumptions:

	Three Months Ended June 30,				Six Months Ended June 30,
	2015		2014		2015		2014
Expected volatility	43	%	44	%	43	%	43	%
Expected life	6 years		6 years		6 years		6 years
Risk-free interest rate	1.69	%	1.86	%	1.69	%	1.80	%
Dividend yield	—		—		—		—

Summary of activities and changes in stock option plans

The following table summarizes the status of the Company's stock options as of June 30, 2015, and changes during the six months then ended (in thousands, except per share data):

	Number of Shares		Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (years)	Aggregate Intrinsic Value
Outstanding at January 1, 2015	2,330		$	18.93
Granted	106		50.71
Exercised	(356	)	14.61
Forfeited	(64	)	12.93
Expired	(1	)	0.31
Outstanding at June 30, 2015	2,015		$	21.56	6.26	$	67,629
Exercisable at June 30, 2015	1,415		$	13.79	5.34	$	57,663
Vested and expected to vest at June 30, 2015	1,966		$	20.85	6.19	$	67,226

Summary of nonvested restricted stock awards

The following table summarizes the status of the Company’s nonvested time-based RSAs and RSUs as of June 30, 2015, and changes during the six months then ended (in thousands, except per share data):

	Number of Shares		Weighted- Average Grant-Date Fair Value
Nonvested at January 1, 2015	1,383		$	30.64
Granted	601		47.44
Vested	(521	)	22.29
Forfeited	(73	)	34.20
Nonvested at June 30, 2015	1,390		$	40.85

Fair value of TSR PBRSUs

:

	2015 TSR PBRSUs		2014 TSR PBRSUs
Expected volatility - Medidata	46	%	52	%
Expected volatility - comparison index	41	%	13	%
Expected life	2.88 years		0.89 years
Risk-free interest rate	0.99	%	0.12	%
Dividend yield	—		—

Summary of performance-based restricted stock units based on expected performance

The following table summarizes the status of the Company’s PBRSUs based upon expected performance as of June 30, 2015, and changes during the six months then ended (in thousands, except per share data):

	Revenue		TSR		Long-Term		Other	Total Number of Shares		Weighted-Average Grant Date Fair Value
Nonvested at January 1, 2015	303		151		1,115		9	1,578		$	27.42
Granted (based on performance at 100% of targeted levels)	—		242		—		—	242		66.99
Adjustment related to expected performance	—		66		(73	)	—	(7	)	44.87
Vested	(151	)	(76	)	—		—	(227	)	26.33
Forfeited	(16	)	(23	)	(8	)	—	(47	)	38.96
Nonvested at June 30, 2015	136		360		1,034		9	1,539		$	35.44

Fair value of employee stock purchase plan shares

The fair value of ESPP shares was estimated using the Black-Scholes pricing model with the following weighted-average assumptions:

	Three Months Ended June 30,				Six Months Ended June 30,
	2015		2014		2015		2014
Expected volatility	51	%	49	%	51	%	49	%
Expected life	1.56 years		1.22 years		1.56 years		1.22 years
Risk-free interest rate	0.35	%	0.21	%	0.35	%	0.21	%
Dividend yield	—		—		—		—