Equity (Tables)

3 Months Ended

Mar. 31, 2014

Equity [Abstract]

Stock Options Activity

Activity with respect to the stock options is summarized as follows:

	Number  of Shares		Weighted- Average Exercise Price		Weighted-Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value
Outstanding at January 1, 2014	15,375,960		$	2.46
Granted	2,094,369		7.29
Exercised	(317,193	)	1.42
Unvested options forfeited	(10,833	)	1.24
Vested options expired	—		—
Outstanding at March 31, 2014	17,142,303		3.07		7.8	$	55,171,947
Vested at March 31, 2014	8,777,850		1.69		6.8	38,950,079
Vested or expected to vest at March 31, 2014 (a)	16,742,166		$	3.01	7.7	$	54,754,819

(a) Includes forfeiture adjusted unvested shares.

Stock Options Outstanding and Exercisable

Following is a summary of stock options outstanding and exercisable at March 31, 2014:

	Options Outstanding				Options Exercisable
Range of Exercise Prices	Number outstanding	Weighted-Average Remaining Contractual Term (in years)	Weighted- Average Exercise Price		Number Exercisable	Weighted- Average Exercise Price
$0.50 - $0.76	1,165,935	3.9	$	0.66	1,165,935	$	0.66
$0.87 - $1.35	6,364,011	7.4	1.20		4,791,313	1.20
$1.40 - $2.29	1,571,700	5.8	1.64		1,321,698	1.66
$2.33 - $3.75	2,042,318	8.5	2.75		605,964	2.77
$3.95 - $5.99	3,263,670	9.0	5.08		892,940	4.99
$6.02 - $8.34	2,734,669	9.3	7.09		—	—
	17,142,303	7.8	$	3.07	8,777,850	$	1.69

Fair Value of Options, Valuation Assumptions

The assumptions used in calculating the fair value of options using the Black-Scholes-Merton option-pricing model are set forth in the following table:

	Three Months Ended March 31,
	2014		2013
Expected volatility	64.1	%	64.3	%
Expected life (in years)	6		6
Expected dividend yield	—		—
Risk-free interest rate	1.69% - 1.96%		0.98%-1.86%

Restricted Stock Awards Roll Forward

Activity with respect to restricted stock awards is summarized as follows.  

	Number of Shares		Weighted-Average Grant Date Fair Value
Unvested at December 31, 2013	576,550		$5.53
Granted	448,864		7.25
Vested	(83,330	)	5.07
Forfeited	—		—
Unvested at March 31, 2014	942,084		$6.39

Allocation of Share-based Compensation

For the three months ended March 31, 2014 and 2013, the Company recognized stock-based compensation as follows: 

	Three Months Ended March 31,
	2014		2013
Cost of sales	$	97,516	$	50,162
Research and development	159,686		75,978
Selling, general and administrative	2,115,162		858,652
	$	2,372,364	$	984,792

Summary of Warrants Outstanding

Following is a summary of the warrant activity for the three months endedMarch 31, 2014:

	Number  of Warrants		Weighted-Average Exercise Price per warrant
Warrants outstanding at January 1, 2014	1,284,816		$	0.90
Warrants exercised	(1,017,000	)	0.76
Warrants outstanding at March 31, 2014	267,816		$	1.44